Recent progress in understanding the persistent luminescence in SrAl2O4:Eu,Dy

Virginija Vitola, Donats Millers, Ivita Bite, Krisjanis Smits & Agnese SpustakaEver since the discovery of SrAl2O4:Eu,Dy persistent afterglow material,that can intensively glow up to 20h, the mechanism of long-lasting luminescence has been a popular area of research. The research is focused on discovering the mechanism of persistent luminescence in order to prolong the duration and intensity of afterglow in a controlled way. Although most researchers agree on the  general things, there are still many unclarities and ambiguities to discuss upon.This review paper briefly sketches in the highlights of past research on the luminescence mechanism in SrAl2O4:Eu,Dy, mainly focusing on the research conducted in the past decade dedicated to clearing these ambiguities.This paper provides an overview of the latest persistent luminescence mechanisms offered by researchers.

Keywords: Persistent luminescence, long afterglow, luminescence mechanism, luminescence mechanism; strontium aluminate

Published in Materials Science and Technology

 

Luminescence of localized states in oxidized and fluorinated silica glass

A.N.Trukhin

Photoluminescence of nominally pure oxidized and fluorinated silica glasses, which have good optical transparency in the optical gap, has been investigated under excitation by excimer lasers. The data are compared with the data for chlorinated silica glass, as well as glass containing OH. The excitation of localized states provides the release and capture of charge carriers, despite the low absorption coefficient. The holes are self-trapped. The recombination in the thermally activated or tunnel process creates luminescence of oxygen-deficient centers. It is concluded that oxidation and fluorination do not change the concentration of localized states, but they change the electronic transitions of the localized states to higher energies. In type III glass with a high OH content, luminescence is suppressed by the presence of hydrogen and appears after irradiation with 7.9 eV photons of the F2 laser. This observation suggests the existence of localized states even in these glasses.

Highlights
• Photoluminescence of oxidized and fluorinated pure silica glasses was studied.
• optical absorption below 8.1 eV is 1–3 cm-1.
• two bands UV and blue luminescence of ODC was observed.
• UV band decay is slower than 4.5 ns and that of blue band is faster than 10 ms.
• recombination process of luminescence excitation.

Keywords
Pure silica glass, Localized states, Self-trapped hole, Recombination luminescence, Oxygen deficient centers, Excimer lasers, Time resolved photoluminescence

Published in Journal of Non-Crystalline Solids

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Short update on ERDF project Phosphorescent coatings prepared by plasma electrolytic oxidation

We are happy to announce that the project ERDF Project Nr.1.1.1.1/16/A/182: “Phosphorescent coatings prepared by plasma electrolytic oxidation (2017-2019)” was successfully evaluated and the green light for the last stage was given. However, although the project is nearing its completion, great amount of work is still required. With finalization of measurements and synthesis, the publications are in active development.

Defending of the doctoral thesis “Electronic excitations and processes in long lasting luminescence material SrAl2O4” – Virgīnija Vītola

Persistent luminescent material SrAl2O4: Eu2+, Dy3+ is widely used and studied for energy efficient applications. A study of SrAl2O4:Eu,Dy; SrAl2O4:Dy,  and undoped SrAl2O4 material was conducted. Improvements for the mechanism of persistent luminescence have been suggested, that involve tunnelling of electron from trapping center to Eu3+, and the proof for stable Dy4+ existence in strontium aluminate has been presented. Undoped material luminescence has been observed, consisting of trace impurity and intrinsic defects luminescence.The results of this work give new knowledge and improve the existing concepts of persistent luminescence in Eu activated strontium aluminates. They also open some possibilities for wider applications of persistent phosphors.

Photoelectric response of localized states in silica glass

A.N.Trukhin

The photoelectric response of pure silica glasses excited by excimer lasers has been studied. The samples were made under various conditions. Photoelectric polarization of samples due to the Dember effect has been registered. The signal was recorded under the conditions of a space charge limited current. The space charge resulting from the capture of electrons and holes creates a static electric field that prevents diffusion of released charge carriers. The current registration in the external circuit stops, despite the continuation of photoexcitation. This effect was used as a fact of measuring the photocurrent in the sample volume instead of the parasitic current that is not associated with the sample. The screen has been chosen to prevent the influence of a spurious signal. It has been found that charge carriers are released when excited in the spectral absorption range of localized states of silica. Based on the Dember effect, the sign of the photoelectric response shows the type of charge carriers – an electron or a hole is mobile. Thus, a sample containing aluminum without alkali ions gives a negative signal, which indicates the diffusion of electrons at 290 K, since aluminum is an effective hole trap. An oxygen-deficient sample at 290 K provides a positive signal indicating the diffusion of holes, because the center of oxygen deficiency is an effective electron trap. This sample at 100 K provides a negative signal due to the effective self-trapping of holes.

Published in Journal of Non-Crystalline Solids

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    Photoluminescence and Electron Spin Resonance of Silicon Dioxide Crystal with Rutile Structure (Stishovite)

    Anatoly Trukhin, Andris Antuzevics

    An electron spin resonance (ESR) and photoluminescence signal is observed in the as grown single crystal of stishovite indicating the presence of defects in the non‐irradiated sample. The photoluminescence of the as received stishovite single crystals exhibits two main bands – a blue at 3 eV and an UV at 4.75 eV. Luminescence is excited in the range of optical transparency of stishovite (below 8.75 eV) and, therefore, is ascribed to defects. A wide range of decay kinetics under a pulsed excitation is observed. For the blue band besides the exponential decay with a time constant of about 18 μs an additional ms component is revealed. For the UV band besides the fast component with a time constant of 1–3 ns a component with a decay in tens μs is obtained. The main components (18 μs and 1–3 ns) possess a typical intra‐center transition intensity thermal quenching. The effect of the additional slow component is related to the presence of OH groups and/or carbon molecular defects modifying the luminescence center. The additional slow components exhibit wave‐like thermal dependences. Photo‐thermally stimulated creation–destruction of the complex comprising host defect and interstitial modifiers explains the slow luminescence wave‐like thermal dependences.

    Published in Physica Status Solidi Applications and Materials Science

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    Creation of glass-characteristic point defects in crystalline SiO2 by 2.5 MeV electrons and by fast neutrons

    Linards Skuja, Nadège Ollier, Koichi Kajihara, Krisjanis Smits

    Point defects in crystalline SiO2, created by 2.5 MeV electron irradiation at dose below the amorphizationthreshold or by fast neutrons, were compared by luminescence spectroscopy. Oxygen dangling bonds (“non-bridging oxygen hole centers”, NBOHCs), peculiar to amorphous state of SiO2, were detected for the first time in electron-irradiated non-amorphized α-quartz crystal. Their presence may signal the formation of nucleation centers in crystal structure as the first step to radiation-induced amorphization. Compared to crystal, irradiated by 1019 cm−2 fast neutrons, their concentration was over 100 times lower, and their inhomogeneous broadening was at least 2.5 times smaller. Divalent silicons (“silicon oxygen deficiency centers”, SiODC(II)), inherent to oxygen-deficient or irradiated SiO2 glass, were detected in neutron-irradiated (1019 n/cm2) α-quartz but were not found after the electron irradiation. Radiation-induced interstitial O2 molecules, characteristic to irradiated glassy SiO2 and other oxide glasses, are found in α-quartz only after neutron irradiation. The oxygen atoms, displaced by the 2.5 MeV e irradiation of α-quartz for fluences up to 1019 e/cm2 evidently stays entirely in the peroxy linkage (Si-O-O-Si bond) form.

    Published in Journal of Non-Crystalline Solids

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    Reversible Photodoping of TiO2 Nanoparticles for Photochromic Applications

    Urmas Joost, Andris Šutka, Marek Oja, Krisjanis Smits, Nicola Döbelin, Ardi Loot, Martin Jarveku,  Mika Hirsimaki, Mika Valden, and Ergo Nõmmiste

    Observations on the strong photochromic effect of crystalline
    TiO2 quantum dots (mean size ≈ 4 nm) are presented. The synthesized
    quantum dots consist of irregularly shaped anatase TiO2 nanoparticles (NPs)
    and are dispersed in butanol (8% by mass). Obtained NPs exhibit a dramatic
    photoresponse to UV light, enabling effective transmittance modulation in a
    broad wavelength range extending from the visible to near-infrared region, and
    even the thermal black body radiation regime beyond 10 μm. The exceptional
    photoresponse is attributed to hole-scavenging by butanol, TiO2 self-reduction,
    injection of electrons to the conduction band, and consequent localized surface
    plasmon resonances in NPs. The observed optical effect is reversible, and the
    initial high transmittance state can be restored simply by exposing the NPs to
    air. The applied NP synthesis route is economic and can be easily scaled for
    applications such as smart window technologies

    Published in Chemistry of Materials

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    Magnetron sputtering fabrication of α-Al2O3:Cr powders and their thermoluminescence properties

    Larisa Grigorjeva, Aleksejs Zolotarjovs, Donats Millers, Krisjanis Smits, Peter Krug, Johannes Stollenwerk, Alan Osman, Thomas Tenostendarp

    For many years doped α-Al2O3 has attracted interest as a dosimeter for personal, environment monitoring and food control. The alumina single crystal growth is a difficult process; however, materials in form of powders, ceramics and coating are possible to obtain. In this study for the first time Cr doped α-Al2O3powders were prepared by DC reactive magnetron sputtering followed by milling and oxidation. The morphology and phase analysis was performed; content of residual impurities was determined and thermostimulated glow curves were measured after different x-ray irradiation times (radiation doses). The prepared powder shows the dosimetry properties up to 20 kGy dose.

    Published in Radiation Measurements

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      EFFECT OF IN DOPING ON THE ZnO POWDERS MORPHOLOGY AND MICROSTRUCTURE EVOLUTION OF ZnO:In CERAMICS AS A MATERIAL FOR SCINTILLATORS

      F. Muktepavela*, J. Maniks, L. Grigorjeva, R. Zabels, P. Rodnyi, E. Gorokhova

      Transparent ZnO ceramics are of interest for use as material for highefficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered ceramics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the transcrystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = Idef/Iexc in comparison with the undoped ceramics. Results characterise ZnO:In ceramics with improved GBs properties as a prospective material for scintillators.

      Published in LATVIAN JOURNAL OF PHYSICS AND TECHNICAL SCIENCES

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      A comparative study of photocatalytically active nanocrystalline tetragonal zyrcon-type and monoclinic scheelite-type bismuth vanadate

      Slobodan D.Dolić, Dragana J.Jovanović, Krisjanis Smits, Biljana Babić, Milena Marinović-Cincović, Slavica Porobić, Miroslav D.Dramićanin

      Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.

      Published in Ceramics International

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      Solvothermal synthesis derived Co-Ga codoped ZnO diluted magnetic degenerated semiconductor nanocrystals

      Andris Šutka, Tanel Käämbre, Urmas Joost, Kuno Kooser, Mati Kook, Roberto Felix Duarte, Vambola Kisand, Mikhael Maiorov, Nicola Döbelin, Krisjanis Smits

      Here we are reporting solvothermal synthesis derived diluted magnetic and plasmonic Co-Ga co-doped ZnOnanocrystals with high magnetization values (from 1.02 to 4.88 emu/g) at room temperature. Co-Ga co-doped ZnO nanocrystals show up to 2 fold increase in saturation magnetization compared to Co doped ZnO nanocrystals at the same Co concentration, with the observed room temperature magnetization higher than previously reported values for multifunctional magnetic and plasmonic nanocrystals, and the effect of Ga suggesting some role of the correspondingly introduced itinerant charge. While at the lowest Ga content the nanoparticles appear homogeneously doped, we note that already a moderate Ga content of several percent triggers a fraction of Co to segregate in metallic form in the bulk of the nanoparticles. However, the amount of segregated Co is not sufficient to account for the total effect, whereas a dominating contribution to the observed magnetism has to be related to itinerant charge mediated exchange interactions.

      Published in Journal of Alloys and Compounds

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      Phase stability and oxygen-sensitive photoluminescence ofZrO2:Eu,Nb nanopowders

      Valter Kiisk,*, Laurits Puust, Hugo Mandar, Peeter Ritslaid, Mihkel Rahn,Ivita Bite, Dzidra Jankovica, Ilmo Sildos, Raivo Jaaniso

      We studied structure and oxygen-sensitive photoluminescence (PL) of ZrO2:Eu,Nb nanocrystalline powders synthesized via a sol-gel route and heat-treated up to 1200 °C. The material containing only 2 at% Eu3+ was predominantly monoclinic, whereas 8 at% of Eu3+ stabilized tetragonal phase. Comparable amount of niobium co-doping effectively suppressed the formation of tetragonal phase.

      PL of Eu3+ ions was observed under direct excitation at 395 nm. PL decay kinetics showed that the luminescence was partially quenched, depending on doping concentrations and ambient atmosphere. At 300 °C, the PL intensity of all samples systematically responded (with up to 70% change) to changing oxygen content in the O2/N2 mixture at atmospheric pressure. At low doping levels, the dominant factor controlling the PL intensity was an energy transferfrom excited PL centers to randomly distributed defects in the ZrO2 lattice. We argue that the charge transfer between the defects and adsorbed oxygen molecules alters the ability of the defects to quench Eu3+ luminescence. At high doping levels, another type of sensor response was observed, where some Eu3+emitters are effectively switched on or off by the change of ambient gas. A remarkable feature of the studied material is a reversing of the sensor response with the variation of the Nb concentration.

      Published in Materials Chemistry and Physics

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      Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ phosphors under 808 nm excitation

      Dragana J.Jovanović, Tamara V.Gavrilović, Slobodan D.Dolić, Milena Marinović-Cincovi, KrisjanisSmits, Miroslav D.Dramićanin

      In recent years, there exists a tendency in research of up-conversion materials to shift excitation from 980 nm to shorter wavelengths. Here, in order to produce up-conversion luminescence emission of GdVO4-based materials under 808 nm excitation, polycrystalline powders of GdVO4:Er3+/Nd3+ and GdVO4:Ho3+/Nd3+ were successfully prepared by a high-temperature solid-state reaction technique. The prepared powders were highly crystalline with a single-phase zircon-type GdVO4 structure and consisted of micrometer-sized irregular spherical particles (2–6 μm in diameter). In all studied samples, visible up-conversion luminescence was successfully achieved under 808 nm illumination. Near-infraredpumping produced emission bands in the green, yellow-orange and green regions of the visible spectrum. The bands in the green and red regions of GdVO4: Er3+/Nd3+ as well as GdVO4:Ho3+/Nd3+ were, respectively, characteristic of Er3+ and Ho3+ ions. The dominant band originating from the 4G7/2 → 4I11/2transition in Nd3+ ions was observed around 597 nm in all samples.

      Published in Optical Materials

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      Mechanical reinforcement of electrospun poly(vinyl alcohol) by α‐FeOOH nanowires

      Anna Šutka Martin Järvekülg Andris Šutka Ivo Heinmaa Uno Mäeorg Krisjanis Smits Martin Timusk

      We report the mechanical performance of α‐FeOOH nanowire reinforced poly(vinyl alcohol) (PVA) composite nanofiber mat, fabricated using straightforward aqueous processing methods. Goethite (α‐FeOOH) nanocrystals have a high elastic modulus and –OH rich surface, ensuring strong interactions with hydrophilic polymers and effective reinforcement. Needle‐less electrospinning resulted in alignment of the nanowires along fibre axis, as confirmed by transmittance electron microscopy studies. Produced composite PVA nanofibers containing 10 wt% goethite nanoparticles exhibited an outstanding fivefold increase in Young’s modulus and 2.5‐fold improvement of tensile strength compared to mats of neat PVA. The addition of α‐FeOOH had a significant influence on glass transition temperature indicating formation of interphase regions around nanowire inclusions. Observed properties are explained by nanowire grafting in the precursor solution, extensive interactions between the adsorbed PVA chains and the matrix and percolation of interphase regions at 10 wt% α‐FeOOH. POLYM. COMPOS., 39:2461–2468, 2018. © 2016 Society of Plastics Engineers

      Published in Polymer Composites

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      Excitation Transfer Engineering in Ce-Doped 2 Oxide Crystalline Scintillators by Codoping with Alkali3 Earth Ions

      Etiennette Auffray, Ramunas Augulis, Andrei Fedorov, Georgy Dosovitskiy, Larisa Grigorjeva, Vidmantas Gulbinas, Merry Koschan, Marco Lucchini, Charles Melcher, Saulius Nargelas, Gintautas Tamulaitis, Augustas Vaitkevicius, Aleksejs Zolotarjovs, and Mikhail Korzhik*

      Time-resolved spectroscopic study of the photoluminescence response to femtosecond pulse excitation and free carrier absorption at different wave10 lengths, thermally stimulated luminescence measurements and investigation of differential absorption are applied to amend the available data on excitation transfer in GAGG:Ce scintillators, and an electronic energy-level diagram in this single crystal is suggested to explain the influence of codoping with divalent Mg on luminescence kinetics and light yield. The conclusions are generalized by comparison of the influence of aliovalent doping in garnets (GAGG:Ce) and oxyorthosilicates (LSO:Ce and YSO:Ce). In both cases, the codoping facilitates the energy transfer to radiative Ce3þ centers, while the light yield is increased in the LYSO:Ce system but reduced in GAGG:Ce.

      Published in Physica Status Solidi

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      Aqueous synthesis of Z-scheme photocatalyst powders and thin-film photoanodes from earth abundant elements

      A.Šutka, M.Vanags, U.Joost, K.Šmits, J.Ruža, J.Ločs, J.Kleperis, T.Juhna

      Solid-state narrow band gap semiconductor heterostructures with a Z-scheme charge-transfer mechanism are the most promising photocatalytic systems for water splitting and environmental remediation under visible light. Herein, we construct all-solid Z-scheme photocatalytic systems from earth abundant elements (Ca and Fe) using an aqueous synthesis procedure. A novel Z-scheme two-component Fe2O3/Ca2Fe2O5 heterostructure is obtained in a straightforward manner by soaking various iron-containing nanoparticles (amorphous and crystalline) with Ca(NO3)2 and performing short (20 min) thermal treatments at 820 °C. The obtained powder materials show high photocatalytic performances for methylene blue dye degradation under visible light (45 mW/cm2), exhibiting a rate constant up to 0.015 min−1. The heterostructure exhibits a five-fold higher activity compared to that of pristine hematite. The experiments show that amorphous iron-containing substrate nanoparticles trigger the Fe2O3/Ca2Fe2O5 heterostructure formation. We extended our study to produce Fe2O3/Ca2Fe2O5nanoheterostructure photoanodes via the electrochemical deposition of amorphous iron-containing sediment were used. The visible-light (15 mW/cm2) photocurrent increases from 183 μA/cm2to 306 μA/cm2 after coupling hematite and Ca2Fe2O5. Notably, the powders and photoanodes exhibit distinct charge-transfer mechanisms evidenced by the different stabilities of the heterostructures under different working conditions.

      Published in Journal of Environmental Chemical Engineering

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      Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

      Tamara Gavrilovića, Jovana Perišaa, Jelena Papana, Katarina Vukovića, Krisjanis Smits,Dragana J. Jovanovića, Miroslav D. Dramićanina

      This paper provides the detailed study of (nano)particle’s size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultrasmall spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5 D0→7 F1), at 612 nm ( 5 D0→7 F2), at 652 nm (5 D0→7 F3) and at 684 nm (5 D0→7 F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle’s morphology.

      Published in Journal of Luminescence

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      Synthesis, structure and spectroscopic properties of luminescent GdVO 4 :Dy 3+ and DyVO 4 particles

      Dragana J. Jovanovic, Andrea Chiappini, Lidia Zur, Tamara V. Gavrilovic, Thi Ngoc Lam Tran, Alessandro Chiasera, Anna Lukowiak, Krisjanis Smits, Miroslav D. Dramicanin, Maurizio Ferrari

      In this work, we focused on the syntheses, structure and spectroscopic properties of GdVO4:Dy3þ and DyVO4 (nano)particles of different sizes and shapes (spherical nanoparticles of 2 nm, 4 nm, and 20 nm in size, nanorods with a few nanometers in diameter and up to 10e20 nm in length and microparticles of 1 e8 mm) obtained by four synthetic methods. The size effect on the structure, Raman active modes, and photoluminescence emission intensities was analyzed by X-ray diffraction, Raman and photoluminescence spectroscopy, scanning and transmission electron microscopy, and diffuse reflection spectroscopy. All X-ray diffraction patterns clearly indicated presence of a single tetragonal zircon-type phase; absence of impurity phases indicate that the dopant Dy3þ ions were successfully and uniformly incorporated into the GdVO4 host lattice due to the equal valence and similar ionic radii. Micro-Raman measurements support the XRD measurements and showed Raman-active modes of the REVO4 systems (RE ¼ Gd, Dy). The difference between the two hosts in the diffuse reflectance spectra was observed and it could be attributed to more effective Gd3þ ions on the charge transfer bands and different polarization (compared to bulk material) in smaller nanoparticles. Photoluminescence spectroscopy showed several bands in the visible and near-infrared regions which can be exclusively attributed to the fef transitions of Dy3þ ions.

      Published in Optical Materials

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      Towards metal chalcogenide nanowire-based colour-sensitive photodetectors

      Edgars Butanovs*, Jelena Butikova, Aleksejs Zolotarjovs, Boris Polyakov

      In recent years, nanowires have been shown to exhibit high photosensitivities, and, therefore are of
      interest in a variety of optoelectronic applications, for example, colour-sensitive photodetectors. In this
      study, we fabricated two-terminal PbS, In2S3, CdS and ZnSe single-nanowire photoresistor devices and
      tested applicability of these materials under the same conditions for colour-sensitive (405 nm, 532 nm
      and 660 nm) light detection. Nanowires were grown via atmospheric pressure chemical vapour transport
      method, their structure and morphology were characterized by scanning and transmission electron
      microscopy (SEM and TEM), X-ray diffraction (XRD), and optical properties were investigated with
      photoluminescence (PL) measurements. Single-nanowire photoresistors were fabricated via in situ
      nanomanipulations inside SEM, using focused ion beam (FIB) cutting and electron-beam-assisted platinum welding; their current-voltage characteristics and photoresponse values were measured. Applicability of the tested nanowire materials for colour-sensitive light detection is discussed.

      Published in Optical Materials

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      Effect of Ga content on luminescence and defects formation processes in Gd3(Ga,Al)5O12:Ce single crystals

      L. Grigorjeva, K. Kamada, M. Nikl, A. Yoshikawa, S. Zazubovich, A. Zolotarjovs

      Luminescence characteristics of Ce3+ – doped Gd3GaxAl5-xO12 single crystals with different Ga contents (x = 1, 2, 3, 4, 5) are studied in the 9-500 K temperature range. The spectra of the afterglow, photoluminescence, radioluminescence, and thermally stimulated luminescence (TSL) of each crystal coincide. The increase of the Ga content results in the high-energy shift of the spectra while the radioluminescence intensity at 9 K remains practically constant up to x = 4. No Ce3+ emission is observed in case of x =5. The total TSL intensity drastically increases, reaches the maximum value around x =2e3, and then decreases due to the thermal quenching of the Ce3+ emission. The TSL glow curve maxima are gradually shifting to lower temperatures, and the dependence of the maxima positions and the corresponding trap depths on the Ga content is close to linear. However, the activation energy of the TSL peaks creation under irradiation of the crystals in the 4f – 5d1 absorption band of Ce3+ decreases drastically with the increasing Ga content (especially in the range of x = 1-2), and this dependence is found to be strongly nonlinear. Possible reasons of the nonlinearity are discussed.

      Published in Optical Materials

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      An important scientific achievement in Latvia 2018

      Our work “A new energy efficient method for acquiring long lasting phosphorescent coatings on metals” which we have carried out as a part of the ERDF project Nr. 1.1.1.1/16/A/182 “Phosphorescent coatings prepared by plasma electrolytic oxidation” has been announced  as one of the most important scientific achievements in Latvia in 2018 by the Latvian Academy of Sciences.

      Teksta latviskotā versija pieejama: http://www.lum.lv/2018-gada-sasniegums-latvijas-zinatne/

      Publikācija par jaunu metodi fosforiscējošo pārklājumu izveidei uz alumīnija virsmas

      Mēs ar lepnumu paziņojam, ka oktobrī Materials & Design tika publicēta jaunā publikācija “Jauna metode fosforiscējošo pārklājumu izveidei uz alumīnija virsmas.” Šo publikāciju finansēja ERAF projekts “Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā” Nr.1.1.1.1/16/A/182 .

      Jauna metode fosforiscējošo pārklājumu izveidei uz alumīnija virsmas

      Jauna metode fosforiscējošo pārklājumu izveidei uz alumīnija virsmas

      Autori: Ivita Bite, Guna Krieke, Aleksejs Zolotarjovs, Katrina Laganovska, Virginija Liepina, Krisjanis Smits, Krisjanis Auzins,Larisa Grigorjeva, Donats Millers un Linards Skuja

      Šis pētījums piedāvā jaunu pieeju fosforescējošu pārklājumu radīšanai uz metāla virsmām. Stroncija alumināti ir vispopulārākie modernie luminiscējoši materiāli, kuri izrāda ilgu pēcspīdēšanu istabas temperatūrā un plašu spektrālo sadalījumu redzamajā diapazonā. Tomēr, neraugoties uz lielo pētījumu skaitu, šādu materiālu sintēzes metodes joprojām ir relatīvi neefektīvas un videi nedraudzīgas. Ilgas pēcspīdēšanas pārklājumi, kas satur SrAl2O4: EU2 +, Dy3 + ir tikuši sagatavoti ar plazmas elektrolītiskās oksidācijas metodi uz komerciālā alumīnija sakausējuma Al6082 virsmas. Šajā procesā esošo elektrisko izlāžu rezultātā stroncija alumināts veidojas līdzīgi kā cietvielu reakcijas metodēs. Rentgenstaru difrakcijas analīze apstiprina, ka pārklājumā ir monoklīniskā SrAl2O4 fāze. Iegūtā pārklājuma optiskās īpašības tika analizētas ar luminiscences metodēm, ko klasiski izmanto luminoforu pētījumos. Pārklājuma veiktspēju salīdzināja ar komerciāli pieejamu stroncija alumināta pulveri. Piedāvātā pārklājuma sintēzes metode var būt noderīga, lai izstrādātu energoefektīvu un ilgstošu automobiļu un sabiedrības drošības infrastruktūru.

      Atslēgvārdi: fosforiscējošais pārklājums, strioncija alumināts, pēcspīdēšana, luminofors, elektrolītiskā oksidācija

      Žurnāls: Materials & Design

      https://doi.org/10.1016/j.matdes.2018.10.021

       Lejupielādēt PDF

      Novel method of phosphorescent strontium aluminate coating preparation on aluminum

      Author list: Ivita Bite, Guna Krieke, Aleksejs Zolotarjovs, Katrina Laganovska, Virginija Liepina, Krisjanis Smits, Krisjanis Auzins,Larisa Grigorjeva, Donats Millers and Linards Skuja

      This study presents a novel approach to produce phosphorescent coatings on metal surfaces. Strontium aluminates are the most popular modern phosphorescent materials exhibiting long afterglow at room temperature and a broad spectral distribution of luminescence in the visible range. However, despite a large amount of research done, methods for synthesis of such materials remain relatively energy inefficient and environmentally unfriendly. A long-afterglow luminescent coating containing SrAl2O4:Eu2+, Dy3+ is prepared by the plasma electrolytic oxidation on the surface of commercial aluminum alloy Al6082. During the electrical discharges in this process, the strontium aluminate is formed in a similar way to the solid-state reaction method. X-ray powder diffraction analysis confirms that the monoclinic SrAl2O4 phase is present in the coating. Optical properties of the obtained coating were analyzed with luminescence methods classically used for studies of luminophores. The performance of the coating was compared with commercially available strontium aluminate powder. The proposed method of coating synthesis may be of value for the development of energy-efficient and long-lasting automotive and public safety infrastructure.

      Keywords: phosphorescent coating, strontium aluminate, long afterglow, persistent luminophore, electrolytic oxidation

      Published in Materials & Design

      https://doi.org/10.1016/j.matdes.2018.10.021

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      A publication in Materials & Design presenting a novel method of phosphorescent strontium aluminate coating preparation on aluminum

      We are proud to announce that a new publication “Novel method of phosphorescent strontium aluminate coating preparation on aluminum” has been written and published in Materials & Design in October. This publication was funded by the ERDF project “Phosphorescent coatings prepared by plasma electrolytic oxidation” No: Nr.1.1.1.1/16/A/182.

      Novel method of phosphorescent strontium aluminate coating preparation on aluminum

      Teksta latviskotā versija pieejama http://www.lum.lv/publikacija-par-jaunu-metodi-fosforiscejoso-parklajumu-izveidei-uz-aluminija-virsmas/

      Participation in AMT and LumDeTr

      In August we participated in the student oriented conference AMT (Advanced Materials and Technologies) in Palanga, Lithuania, presenting multiple posters and attending the lectures.

      Just last week we also participated in the LumDeTr (Luminescent Detectors and Transformers of Ionizing Radiation) conference in Prague, Czech Republic. We would like to acknowledge the Mobility Financial Support received from the Faculty of Physics, Mathematics and Optometry, University of Latvia, which partially funded the attendance of this conference.

      Niobium enhanced Europium ion luminescence in Hafnia nanocrystals

      K. Laganovska*, I. Bite, A. Zolotarjovs, K. Smits

      In this work we demonstrate a method where by adding Nb ions, Ln3+ ion lumi
      nescence intensity in HfO2 is increased for up to 15 times (in a sample containing
      5mol%Eu). The effect is described as niobium acting as a charge compensator and neutralizing the charge resulting from Ln3+ ion insertion in Hf4+ site and
      hence reducing the number of defects present. This is the second system where
      such an effect was observed, so it is expected that other metal oxides would show the same effect. The optical properties of HfO2:Eu3+ and HfO2:Eu3+, Nb5+,
      synthesized using the sol-gel method and annealed at various temperatures are
      studied. A conclusion that the structure of hafnia does not affect luminescence
      intensity directly and a larger role is played by factors such as defect presence
      and the size of the particles is drawn based on XRD and TSL measurements.
      Time-resolved luminescence measurements were also carried out and significant
      changes depending on dopant concentration and annealing temperatures were
      observed. Judd Ofelt theory was used to determine quantum efficiency and the local symmetry of Eu3+ ion sites.
      Keywords: Hafnia, Luminescence, Eu3+, Charge compensation, Judd Ofelt

      Published in Journal of Luminescence

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      The search for defects in undoped SrAl2O4 material

      A new publication in the frame of ERDF Project Nr.1.1.1.1/16/A/182 on fundamental processes in phosphorescent materials has been published.

      Virginija Vitola, Donats Millers, Krisjanis Smits, Ivita Bite, Aleksejs Zolotarjovs

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. The luminescence properties and the possible luminescence mechanism of this material have been studied extensively, but there is almost no information available about the undoped material. Therefore, this article deals with the luminescence and thermally stimulated luminescence of an undoped SrAl2O4, revealing the possible defects that might be involved in the creation of the long afterglow in doped material. We conclude that undoped material exhibits some luminescence under X-ray irradiation in low temperature; close to room temperatures luminescence is almost fully thermally quenched in comparison to low temperatures. We can observe F and F2 center luminescence as wellas trace metal luminescence inthe emission spectrum.TSL glow curveyields the peaksthat are close to those observed in material with Eu and Dy doping; therefore these peaks are clearly related to intrinsic defects. The peak at around 400K, that is shifting with rare earth doping, might be due to dopant interaction with intrinsic defects.

      Published in Optical Materials

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      Teksta latviskotā versija pieejama šeit: http://www.lum.lv/defektu-noteiksana-nedopeta-sral2o4-materiala/

      The search for defects in undoped SrAl2O4 material

      Virginija Vitola, Donats Millers, Krisjanis Smits, Ivita Bite, Aleksejs Zolotarjovs

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. The luminescence properties and the possible luminescence mechanism of this material have been studied extensively, but there is almost no information available about the undoped material. Therefore, this article deals with the luminescence and thermally stimulated luminescence of an undoped SrAl2O4, revealing the possible defects that might be involved in the creation of the long afterglow in doped material. We conclude that undoped material exhibits some luminescence under X-ray irradiation in low temperature; close to room temperatures luminescence is almost fully thermally quenched in comparison to low temperatures. We can observe F and F2 center luminescence as wellas trace metal luminescence inthe emission spectrum.TSL glow curveyields the peaksthat are close to those observed in material with Eu and Dy doping; therefore these peaks are clearly related to intrinsic defects. The peak at around 400K, that is shifting with rare earth doping, might be due to dopant interaction with intrinsic defects.

      Published in Optical Materials

       

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      High resolution luminescence spectroscopy and thermoluminescence of different size LaPO4:Eu3+ nanoparticles

      Tamara Gavrilovića,  Katrīna Laganovska, Aleksejs Zolotarjovs, Krisjanis Smits, Dragana J. Jovanović, Miroslav D. Dramićanin

      Nanoparticles (5nm) and nanorods (2nm×15nm and 4nm×20nm) of monoclinic monazite LaPO4:Eu3+ were prepared by reverse micelle and co-precipitation techniques. Effects of the particle size and surface defects on the intensity of luminescence and the emission spectrum shapes were analyzed by high resolution spectroscopy under laser (266nm) and X-rays excitation. All synthesized LaPO4:Eu3+ samples showed similar spectral features with characteristic Eu3+ ions emission bands: 5D0→7F0 centered at 578.4nm, magnetic-dipole transition 5D0→7F1 at 588–595nm, electric-dipole transition 5D0→7F2 at 611.5–620.5nm, 5D0→7F3 at (648–652nm) and 5D0→7F4 at (684–702.5nm), with the most dominant electric-dipole 5D0→7F2 transition. Additionally, the thermally stimulated luminescence was studied for the most dominant peak at 611.5nm. It was shown that the Eu3+ doping creates traps in all samples. Two prominent and well resolved glow peaks at 58.7K and 172.3K were detected for 5nm nanoparticles, while low-intensity glow-peaks at 212.1K and 212.2K were observed in the X-rays irradiated nanorods. Displayed glows could be attributed to free and bound electrons and holes or to the recombination of electrons of ionized oxygen vacancies with photogenerated holes. To obtain information about the processes and specific defect type it is necessary to carry out additional analysis for all synthesized samples. The glow curves were analyzed and trap parameters were estimated and discussed throughout the paper.

      Published in Optical Materials

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      ERDF Project Nr.1.2.1.2 KC-PI -2017/90 Mini spectrometer for food analyses (2018)

      The proposed project aims to create a mini spectrometer for food analysis, which would be affordable, small and multifunctional. Our goal is to offer the parties interested a way to constantly control the quality of their products without buying serious lab equipment or hiring additional staff. The first prototype created will be customized specifically for the beer industry – measuring color, turbidity, bitterness, number of live yeast cells and other properties. The measurement results and other information will be displayed in a mobile application which would be connected to the phone via bluetooth. We aim for the application to be as simple, user friendly and straightforward as possible, so that the users could use it from the get-go. Later on we plan on adapting the device to other industries as well, such as dairy and wine industries, and also individual uses to check for lactose or preservative presence.

       

      Projekta mēķis ir izstrādāt uz spektrofotometrijas balstītu iekārtu pārtikas nozares kvalitātes kontrolei. Lai gan sākotnēji plānots izstrādāt ierīci tieši alus nozarei – krāsas, rūgtuma, duļķainības, rauga veselības u.c. noteikšanai, vēlāk tā tiks papildināta un pielāgota arī citām nozarēm. Ierīces priekšrocības ir tās zemās izmaksas, multifunkcionalitāte, pielāgojamība un mazais izmērs.

      Projekta pirmās kārtas maksimālās kopējās izmaksas ir 25 000 euro ar ERAF atbalsta intensitāti 90%.
      1. kārtas laikā notiek Tirgus izpēte, Tehniski ekonomiskā priekšizpētes un Komercializācijas stratēģijas izstrāde.

      Update on ERDF Project Nr.1.1.1.1/16/A/182

      ERDF Project Nr.1.1.1.1/16/A/182:

      A significant improvement on the control of various electrical parameters was achieved in the last couple of months due to the planned upgrades of the power supply unit. New limits of coating preparation can be achieved now with higher voltages (up to 1000V) as well as with vastly improved software and automated control algorithms allowing uninterrupted change of any desired parameter in time. This modification allows the in-depth studies of effects of high voltage on coating formation process and implementation of RE ions in it. In addition, the stability of the power supply was improved allowing extra-long processing time on high loads. This is important for the different oxide phase formation as recrystallisation occurs only at longer processing times.

      With the new setup a new set of samples was prepared and further optimization of parameters is undergoing. The main aim is to improve PEO coating to match and exceed the performance of similar materials in other forms.

      Teksta latviskotā versija ir atrodama šeit.

      ERAF projekts Nr.1.1.1.1/16/A/182 – Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā – jaunumi

      Pēdējo pāris mēnešu laikā panākts ievērojams uzlabojums procesa elektrisko parametru kontrolē,ko nodrošināja barošanas bloka veiktā modernizācija. PEO iekārtai ir vairāki uzlabojumi ieskaitot augstāku spriegumu limitu (līdz 1000 V), kā arī ar ievērojami vieglāk lietojamu programmatūru un automatizētiem vadības algoritmiem, kas ļauj nepārtraukti mainīt jebkuru vēlamo parametru procesa laikā. Šīs iespējas ļauj padziļināti izpētīt augsta sprieguma ietekmi uz pārklājuma veidošanas procesu un RE jonu ieviešanu tajā. Turklāt tika uzlabota barošanas avota stabilitāte, nodrošinot ilgāku nepārtrauktu apstrādes laiku pie lielām slodzēm. Tas ir svarīgi dažādiem oksīda fāzes veidošanās procesiem, jo pārkristalizācija notiek tikai ilgākos apstrādes laikos.
      Tika sagatavots paraugu komplekts un turpināta parametru optimizācija. Galvenais mērķis ir nemainīgs: uzlabot ilgspīdošu PEO pārklājumu ar kvalitāti, kas sakrīt vai pārsniedz līdzīgu materiālu kvalitāti.

      X-ray excited luminescence of SrAl2O4:Eu,Dy at low temperatures

      A new publication in the frame of ERDF Project Nr.1.1.1.1/16/A/182 on fundamental processes in phosphorescent materials has been published.

      V. Liepina, D. Millers * , K. Smits, A. Zolotarjovs, I. Bite

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. In this study we carried out the study of X-ray excited luminescence of SrAl2O4:Dy and SrAl2O4:Eu,Dy samples, including the measurements of afterglow at low temperatures within extended time scale. We observed both Eu and Dy luminescence peaks in the afterglow and TSL measurements. In recent articles the tunneling of electron from trap levels to excited Eu luminescence center was discussed, and in this research we conclude that under X-ray irradiation Eu2+ and Dy3+ serve as hole traps; electron tunneling is present in both SrAl2O4:Eu, Dy and SrAl2O4: Dy, and luminescence afterglow at 10 K arises from decay of excited Eu2+ and Dy3+ centers created via electron tunneling from host trap to Eu3+ and Dy4+ ions.

      Journal of Physics and Chemistry of Solids

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      Teksta latviskotā versija pieejama šeit: http://www.lum.lv/rentgenstarojuma-ierosinata-sral2o4-luminescence-zemas-temperaturas/

      X-ray excited luminescence of SrAl2O4:Eu,Dy at low temperatures

      V. Liepina, D. Millers * , K. Smits, A. Zolotarjovs, I. Bite

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. In this study we carried out the study of X-ray excited luminescence of SrAl2O4:Dy and SrAl2O4:Eu,Dy samples, including the measurements of afterglow at low temperatures within extended time scale. We observed both Eu and Dy luminescence peaks in the afterglow and TSL measurements. In recent articles the tunneling of electron from trap levels to excited Eu luminescence center was discussed, and in this research we conclude that under X-ray irradiation Eu2+ and Dy3+ serve as hole traps; electron tunneling is present in both SrAl2O4:Eu, Dy and SrAl2O4: Dy, and luminescence afterglow at 10 K arises from decay of excited Eu2+ and Dy3+ centers created via electron tunneling from host trap to Eu3+ and Dy4+ ions.

      Journal of Physics and Chemistry of Solids

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      Jaunumi ERAF Post Doc project No. 1.1.1.2/VIAA/1/16/215: Jauni nanoizmēru oksīdu materiāli ar upconversion luminiscenci

      Mēs esam priecīgi paziņot, ka nesen projektā ir panākts ievērojams progress, un ir tikušas izstrādātas un optimizētas četras dažādas uz fosfātiem un vanadānu balstītas fosforu sagatavošanas metodes: augstas temperatūras, cietvielu, līdz-izgulsnēšanās, reversās micellas un koloidālās ķīmijas.
      Tika iegūti paraugi ar dažādām morfoloģijām un izmēriem ar pietiekamu luminiscences intensitāti. Iekļaujot tos silīcija dioksīda viļņvados, daži no tiem varētu atrast potenciālu pielietojumu 1,3 μm fotoluminiscences uzlabošanā.
      Darbs, kurā pētītas luminiscējošās lantāna nanodaļiņas, tika prezentēts starptautiskajā konferencē ‘’Spectral shaping for biomedical and energy applications’’, SHIFT 2017, 13.-17. Novembris, Tenerife, Spānija.
      Publicēšanai tika pieņemts raksts ar detalizētu pētījumu par nanodaļiņu lieluma ietekmi uz dopēta lantāna un europija fosfāta strukturālajām un optiskajām īpašībām. Raksts ir atrodams tiešsaistē. https://doi.org/10.1016/j.jlumin.2017.12.002 Lepojamies arī ziņot, ka tika iesniegts kopīgs manuskripts no mūsu komandas un pētniekiem no Itālijas, Vjetnamas, Polijas un Serbijas, kuri pētīja fosforus, kuru pamatā ir vanadāta matrica, un pieņemts publicēšanai.
      Mēs turpināsim savu darbu meklējot materiālus ar uzlabotām īpašībām un plašākiem praktiskajiem pielietojumiem.

      Core–Shell Engineering to Enhance the Spectral Stability of Heterogeneous Luminescent Nanofluids

      Lucía Labrador-Páez, Marco Pedroni, Krisjanis Smits, Adolfo Speghini, Francisco Jaque, José García-Solé, Daniel Jaque,* and Patricia Haro-González

      The tendency to the miniaturization of devices and the peculiar properties of the nanoparticles have raised the interest of the scientific community in nanoscience. In particular, those systems consisting of nanoparticles dispersed in fluids, known as nanofluids, have made it possible to overcome many technological and scientific challenges, as they show extraordinary properties. In this work, the loss of the spectral stability in heterogeneous luminescent nanofluids is studied revealing the critical role played by the exchange of ions between different nanoparticles. Such ion exchange is favored by changes in the molecular properties of the solvent, making heterogeneous luminescent nanofluids highly unstable against temperature changes. This work demonstrates how both temporal and thermal stabilities of heterogeneous luminescent nanofluids can be substantially improved by core–shell engineering. This simultaneously avoids the leakage of luminescent ions and the effects of the solvent molecular changes.

      core shell

      Published in Particle & Particle Systems Characterization.

       

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      ERAF Post Doc project No. 1.1.1.2/VIAA/1/16/215: Jauni nanoizmēru oksīdu materiāli ar upconversion luminiscenci

      Galvenā darbības joma:Šis starpdisciplinārais projekts aptver plaši pētītu problēmu risinājumus luminiscējošas augšup-pārveidojošo nanomateriālu jomā. Piemēram, virsmas stabilizācija, modifikācija, (bio) funkcionalizācija un materiālu toksiskums, kā rezultātā tiks izstrādāti un sagatavoti daudzfunkcionāli nanomateriāli ar uzlabotām raksturīpašībām.

      Mūsdienās viena no vissarežģītākajām materiālu zinātnes problēmām ir sintētisko metožu, kas nodrošina augstas fāzes tīrības, kristalitātes, lieluma, morfoloģijas un sastāva vienveidīgumu, optimizācija un attīstība. Lai iegūtu šāda veida neorganiskas augšup-pārveidojošās luminiscējošās nanodaļiņas, tiks izmantotas vairākas atšķirīgas sintēzes metodes: koloidālās ķīmijas metodes, inversās micellas tehnika, līdz-izgulsnēšanās, mikroviļņu hidrotermālais, sol-gel, kūstošā sāls un cietvielu.

      Pētījuma projekta laikā tiks izveidotas, pārklātas un modificētas dažādas luminiscējošas augšup-pārveidojošās nanomateriālu grupas. To vidū ir: metālu oksīdi (TiO2, ZnO, ZrO2, HfO2), alumināti (SrAlO4), silikāti (SrSiO4), fosfāti (APO4, A = La, Y, Gd, Lu), vanadāti (piemēram, GdVO4), fluorīdi (NaYF4 , LaF4) un oksisulfīdi (piemēram, Gd2O2S). Turklāt piedāvātās struktūras var tikt izmantotas kā cietvielu lāzeru pastiprinātāji, pretviltošanas etiķetes, kā arī kontrastviela multimodālajai attēlveidošanai, vēža noteikšanai, fotodinamiskā terapija un zāļu piegāde

      ERAF projekts Nr.1.1.1.1/16/A/182 – Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā – jaunumi

      PEO Projekta izpildē sasniegts nozīmīgs atskaites punkts – pirmo reizi ir iegūti luminiscējoši pārklājumi ar pietiekamu fosforiscences intensitāti, lai to būtu iespējams saskatīt ar neapbruņotu aci. Turpinām darbs pie intensitātes palielināšanas un luminiscences pēcspīdēšanas parametru variēšanas. Sasniegtie rezultāti tiks apkopoti zinātniskajā rakstā.

      Tāpat ir iesniegta publikācija, kurā pētītas stroncija alumināta pulvera optiskās īpašības.

      Sākot ar septembri Boriss Poļakovs un Krišjānis Auziņš ir pievienojušies projekta komandai un aktīvi strādā, lai veicinātu turpmāku projekta veiksmīgu norisi.

      Rezultātu labākai atkārtojamībai, ir veikti uzlabojumi PEO reaktora kamerā (skat. Fotoattēlu), ļaujot pētīt pārklājumus detalizētāk. Tehniskie uzlabojumi ir veikti arī pašos alumīnija paraugos – sagatavēs. Jaunā tipa standartizētos paraugus ir iespējams sadalīt mazākās daļās, pilnībā izslēdzot parauga virsmas nejaušu bojāšanu dalīšanas procesā.

      Project ERDF Project Nr.1.1.1.1/16/A/182: Phosphorescent coatings prepared by plasma electrolytic oxidation update

      PEO A certain project milestone has been recently achieved and luminescent coatings with sufficient luminescence intensity to be seen by the naked eye have been acquired. We will continue our work on intensity and luminescence afterglow parameter improvement and it certainly looks like we’re moving in the right direction although of course there’s tons of work still ahead of us.

      A publication studying optical properties of strontium aluminate has been submitted and is being reviewed.

      We’re also happy to announce that starting September Boriss Poļakovs and Krišjānis Auziņš have joined the project and are actively working to contribute to project’s successful ongoing.

      Improvements on PEO reactor chamber (see photo) have been  made to insure better repeatability and constant results, allowing to study the coatings with greater detail and less errors. Technical improvements have also been made to aluminum samples – it is now possible to split the samples into smaller pieces with absolutely no potential damage to the coating.

      Teksta latviskotā versija pieejama šeit. 

       

      Taking part in the new COST Actions

      Our leading researcher, Krisjanis Smits, was entitled to represent Latvia in two COST actions:

                   1.CA COST Action CA16215
                   European network for the promotion of portable, affordable and simple analytical platforms

                   2.CA COST Action CA15107
                   Multi-Functional Nano-Carbon Composite Materials Network (MultiComp)

      PROMES CNRS visit

      Our team is visiting PROMES CNRS facilities (Font-Romeu, France). We are grateful for the access to the facilities in frame of SFERA 2 project. This great opportunity will be used to prepare samples for the successful realization of ERDF Project Nr.1.1.1.1/16/A/182.

      IMG-20170724-WA0000

      Unveiling Molecular Changes in Water by Small Luminescent Nanoparticles

      Lucía Labrador-Páez, Dragana J. Jovanovic´, Manuel I. Marqués, Krisjanis Smits,
      Slobodan D. Dolic´, Francisco Jaque, Harry Eugene Stanley, Miroslav D. Dramic´anin,
      José García-Solé, Patricia Haro-González, and Daniel Jaque*

      Nowadays a large variety of applications are based on solid nanoparticles dispersed in
      liquids—so called nanofluids. The interaction between the fluid and the nanoparticles
      plays a decisive role in the physical properties of the nanofluid. A novel approach
      based on the nonradiative energy transfer between two small luminescent nanocrystals
      (GdVO4:Nd3+ and GdVO4:Yb3+) dispersed in water is used in this work to investigate
      how temperature affects both the processes of interaction between nanoparticles and
      the effect of the fluid on the nanoparticles. From a systematic analysis of the effect
      of temperature on the GdVO4:Nd3+ → GdVO4:Yb3+ interparticle energy transfer, it
      can be concluded that a dramatic increase in the energy transfer efficiency occurs for
      temperatures above 45 °C. This change is properly explained by taking into account
      a crossover existing in diverse water properties that occurs at about this temperature.
      The obtained results allow elucidation on the molecular arrangement of water
      molecules below and above this crossover temperature. In addition, it is observed
      that an energy transfer process is produced as a result of interparticle collisions that
      induce irreversible ion exchange between the interacting nanoparticles.

      smits small

      DOI: 10.1002/smll.201700968

      http://onlinelibrary.wiley.com/doi/10.1002/smll.201700968/full

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      Granted access to MSSFs Facility at PROMES, CNRS

      Our group was accepted to access PROMES CNRS solar facilities within the framework of the EU-DG RTD’s project: “The European Solar Research Infrastructure for Concentrated Solar Power. Second Phase – SFERA-II

      We are looking forward to continue research collaboration with the facility and prepare samples for further study.

      sfera logo

      sfera reactor

      Luminescence and Raman Detection of Molecular Cl2 and ClClO Molecules in Amorphous SiO2 Matrix

      Abstract Image

      Chlorine is a common undesirable impurity in synthetic SiO2 glass for ultraviolet optics and optical fibers. It is usually incorporated into glass as bound Si–Cl groups or interstitial Cl2molecules. We report a high-sensitivity detection of Cl2 in amorphous SiO2 (a-SiO2) by photoluminescence (PL) and also by Raman spectroscopy. The Cl2 PL emission band at 1.22 eV (1016 nm) appears at T < 160 K and shows a characteristic vibronic progression with separations ≈(520–540) cm–1 and an average lifetime of ≈5 ms at 13 K. Its excitation spectrum coincides with the shape of the 3.78 eV (328 nm) optical absorption band of Cl2 in a-SiO2, corresponding to the X → A 1Πu transition to repulsive excited state. Direct X → a singlet-to-triplet excitation was also observed at 2.33 eV (532 nm). Cl2 PL may serve as a sensitive and selective tool for monitoring Cl impurities and their reactions in a-SiO2. A Raman band of Cl2 is found at 546 cm–1. Cl2 photodissociation at energies up to 4.66 eV (266 nm) was not detected, pointing to a strong cage effect in a-SiO2 matrix. However, 7.9 eV (157 nm) photolysis of interstitial O2molecules gives rise to a Raman band at 954 cm–1, indicating a formation of dichlorine monoxide isomer, ClClO molecule by reaction of O atoms with interstitial Cl2.

      J. Phys. Chem. C, 2017, 121 (9), pp 5261–5266

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      ERAF projekts -Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā-.

      Līguma numurs 1.1.1.1/16/A/182

      Projekta ilgums: 27.02.2017 -31.10.2019

      Projekta zinātniskais vadītājs: Dr.phys. Krisjanis Smits

       

      Projekta mērķis ir ne-saimnieciskajā rūpnieciskajā pētījumā iegūt alumīniju saturošu fosforiscējošu pārklājumu plazmas elektrolītiskās oksidācijas (PEO) procesā.

      Projekta gaitā paredzēts PEO procesā iegūt leģētus ar Eu joniem aktivētus kompleksos oksīdus, izveidot aktivatoru nanokristālu pārklājumu poru aizpildīšanai un, veicot gala oksidāciju, PEO procesā iegūt luminiscentu pārklājumu. Paralēli veicamajām darbībām, tām tiks pielāgota SIA “ElGoo tech” īpašumā esošā PEO aparatūra un tās parametri, kā rezultātā iegūsim validētu nepatentētu tehnoloģiju. Tiks veikta iegūto materiālu īpašību (luminiscences, struktūras un morfoloģijas) izpēte. Plānots iepirkums, kura nolikumā, vērtēšanā un tehniskajā specifikācijā tiks piemēroti Zaļā publiskā iepirkuma kritēriji un principi.

      Ar saimniecisko darbību nesaistīto projektu plānots īstenot kopā ar sadarbības partneri – komersantu SIA “ElGoo tech” no 2017.gada 1.februāra līdz 2019.gada 31.oktobrim, ar kuru kopā ir izstrādāts šis projekts un noslēgts sadarbības līgums. Plānotās projekta izmaksas ir 539 844.50 EUR.

      Plānots iegūt 120 gab. fosforiscējoša pārklājuma paraugus, vienu šī procesa validētas nepatentētas tehnoloģijas aprakstu, 6 zinātniskos rakstus, piesaistīto privāto finansējumu un 1 komersantu, kurš sadarbojas ar pētniecības organizāciju. Pētījumā tiks nodarbināti vismaz 11 darbinieki, t.sk. 4, kuriem tiks izveidotas jaunas darba vietas.

      Projektu plānots īstenot inovatīvo materiālu un tehnoloģijas nozarē izmantojot starpdisciplinaritāti – dabas zinātnes (1.3 fizika (Physical sciences) un 1.4 ķīmija (Chemical sciences)) un inženierzinātnes un tehnoloģija (2.5 materiālu zinātne (Materials engineering) un 2.10 nanotehnoliģijas (Nano-technology)).

      Tiks pētīta iespēja izveidot luminiscentus pārklājumus, izmantojot plazmas elektroķīmisko oksidāciju (PEO). Patreiz PEO procesā iegūtie pārklājumi tiek aktīvi izmantoti, jo tiem piemīt labas aizsargājošās (liela cietība, laba nodilumizturība, termiskā aizsardzība, pretkorozijas uc.) īpašības. Metālu un dažu tā sakausējumu oksīdiem, ir labas optiskās īpašības, taču, piemēram, luminiscence PEO procesā iegūtiem pārklājumiem iepriekš nav pētīta. Pirmie pētījumi tika veikti SIA “ElGoo tech” sadarbojoties ar LU CFI, kuros iegūti pirmie labi luminiscējošie pārklājumi. Šie rezultāti un literatūrā atrodamie cita veida pētījumi parāda, ka ar PEO metodi iespējams izveidot arī fosforiscentos pārklājums, kuriem būtu ievērojams pielietojumu potenciāls, piemēram, SrAl2O4:Eu:Dy, kuram piemīt vienas no lielākajām kvantu efektivitātēm un ilgākā pēcspīdēšana.

      Tādēļ šī pētījumu projekta ietvaros plānots iegūt alumīniju saturošus pārklājumus ar ilgu pēcspīdēšanu (fosforiscenci). Iegūstamie pārklājumi būs caurspīdīgi tuvajā UV apgabalā, tādejādi gala pārklājumam būs vairākas reizes lielāka efektivitāte salīdzinot ar pārdošanā esošajām fosforiscentajām krāsām. vienlaicīgi fosforiscējošais pārklājums kalpos kā metālu atikorozijas pārklājums un šāda pārklājuma noturība, ilgmūžība būs daudz lielāka salīdzinot ar krāsām.

      Projekta sasniegtajiem rezultātiem pēc projekta beigām tiks nodrošināta:

      1. Finansiālā ilgtspēja – no valsts un privātā sektora budžeta tiks finansētas 4 jaunizveidotās darba vietas un finansēta projekta rezultātu publiskā pieejamība, SIA „ElGoo tech” no savas saimnieciskās darbības peļņas uzturēs projektā modificēto PEO aparatūru un budžetā paredzēs realizēt eksperimentālo pētījumu;
      2. Institucionālā ilgtspēja – 4 projektā iesaistītie zinātniskie darbinieki tiks nodarbināti jaunizveidotajās darba vietās, tā saglabājot pētījumā iegūto praktisko pieredzi un zinātību un izmantojot to tālākajā darbā, savukārt projekta īstenotāji (LU CFI un SIA „ElGoo tech”) apņemas pētījuma rezultātus izmantot savā turpmākajā zinātniskajā un saimnieciskajā darbībā;
      3. Politiskā ilgtspēja – ir nodrošināta, jo projekta mērķi atbilst RIS3 noteiktajiem tautsaimniecības transformācijas virzieniem un izaugsmes 1., 2. un 3.prioritātei. Projektu raksturojošie atslēgas vārdi – plazmas elektroķīmiskā oksidācija, pārklājumi, fosforiscence, luminiscence, oksīdi, nanokristāli.

       

      Oficiālā www.CFI.lv lapa par projektu ir atrodama šeit.

      ERDF project -Phosphorescent coatings prepared by plasma electrolytic oxidation-

           

      Project No: Nr.1.1.1.1/16/A/182

      Main scope:

      The proposed project foresees studies of luminescent coatings prepared by plasma electrolytic oxidation (PEO). Up to now, PEO coatings were mostly studied because of their tribological properties; however, PEO coatings also have good wear resistance, high hardness and are chemically stable therefore this technology can be applied to form protective coatings on metals. It is known that many oxide based materials exhibit good luminescent properties; however, the luminescence of PEO produced oxide layers was not studied before. The first research in this direction was made by private company Elgoo tech in cooperation with Insitute of Solid State Physics University of Latvia.

      During the research project, PEO process will be used to produce luminous aluminium coatings. The analysis of accessible data indicates that PEO synthesis is a promising approach for production of materials with long lasting luminescence, for example SrAl2O4:Eu:Dy. The coatings prepared by PEO will be transparent in blue and UV range, therefore the final long lasting luminescence efficiency is expected to be several times higher than that of luminescent paints currently in use. In addition, coatings could serve as protection for metals since the durability of such coatings is expected to be better compared to paints.

      See information in Latvian here!

      See official institute webpage about the project here!

      UPDATES


      Short update on ERDF project Phosphorescent coatings prepared by plasma electrolytic oxidation

      We are happy to announce that the project ERDF Project Nr.1.1.1.1/16/A/182: “Phosphorescent coatings prepared by plasma electrolytic oxidation (2017-2019)” was successfully evaluated and the green light for the last stage was given. However, although the project is nearing its completion, great amount of work is still required. With finalization of measurements and synthesis, the publications are in active development.

      An important scientific achievement in Latvia 2018

      Our work “A new energy efficient method for acquiring long lasting phosphorescent coatings on metals” which we have carried out as a part of the ERDF project Nr. 1.1.1.1/16/A/182 “Phosphorescent coatings prepared by plasma electrolytic oxidation” has been announced  as one of the most important scientific achievements in Latvia in 2018 by the Latvian Academy of Sciences.

      Teksta latviskotā versija pieejama: http://www.lum.lv/2018-gada-sasniegums-latvijas-zinatne/

      A publication in Materials & Design presenting a novel method of phosphorescent strontium aluminate coating preparation on aluminum

      We are proud to announce that a new publication “Novel method of phosphorescent strontium aluminate coating preparation on aluminum” has been written and published in Materials & Design in October. This publication was funded by the ERDF project “Phosphorescent coatings prepared by plasma electrolytic oxidation” No: Nr.1.1.1.1/16/A/182.

      Novel method of phosphorescent strontium aluminate coating preparation on aluminum

      Teksta latviskotā versija pieejama http://www.lum.lv/publikacija-par-jaunu-metodi-fosforiscejoso-parklajumu-izveidei-uz-aluminija-virsmas/

      The search for defects in undoped SrAl2O4 material

      A new publication in the frame of ERDF Project Nr.1.1.1.1/16/A/182 on fundamental processes in phosphorescent materials has been published.

      Virginija Vitola, Donats Millers, Krisjanis Smits, Ivita Bite, Aleksejs Zolotarjovs

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. The luminescence properties and the possible luminescence mechanism of this material have been studied extensively, but there is almost no information available about the undoped material. Therefore, this article deals with the luminescence and thermally stimulated luminescence of an undoped SrAl2O4, revealing the possible defects that might be involved in the creation of the long afterglow in doped material. We conclude that undoped material exhibits some luminescence under X-ray irradiation in low temperature; close to room temperatures luminescence is almost fully thermally quenched in comparison to low temperatures. We can observe F and F2 center luminescence as wellas trace metal luminescence inthe emission spectrum.TSL glow curveyields the peaksthat are close to those observed in material with Eu and Dy doping; therefore these peaks are clearly related to intrinsic defects. The peak at around 400K, that is shifting with rare earth doping, might be due to dopant interaction with intrinsic defects.

      Published in Optical Materials

      Download PDF

      Teksta latviskotā versija pieejama šeit: http://www.lum.lv/defektu-noteiksana-nedopeta-sral2o4-materiala/

      ERAF projekts Nr.1.1.1.1/16/A/182 – Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā – jaunumi

      Pēdējo pāris mēnešu laikā panākts ievērojams uzlabojums procesa elektrisko parametru kontrolē,ko nodrošināja barošanas bloka veiktā modernizācija. PEO iekārtai ir vairāki uzlabojumi ieskaitot augstāku spriegumu limitu (līdz 1000 V), kā arī ar ievērojami vieglāk lietojamu programmatūru un automatizētiem vadības algoritmiem, kas ļauj nepārtraukti mainīt jebkuru vēlamo parametru procesa laikā. Šīs iespējas ļauj padziļināti izpētīt augsta sprieguma ietekmi uz pārklājuma veidošanas procesu un RE jonu ieviešanu tajā. Turklāt tika uzlabota barošanas avota stabilitāte, nodrošinot ilgāku nepārtrauktu apstrādes laiku pie lielām slodzēm. Tas ir svarīgi dažādiem oksīda fāzes veidošanās procesiem, jo pārkristalizācija notiek tikai ilgākos apstrādes laikos.
      Tika sagatavots paraugu komplekts un turpināta parametru optimizācija. Galvenais mērķis ir nemainīgs: uzlabot ilgspīdošu PEO pārklājumu ar kvalitāti, kas sakrīt vai pārsniedz līdzīgu materiālu kvalitāti.

      X-ray excited luminescence of SrAl2O4:Eu,Dy at low temperatures

      A new publication in the frame of ERDF Project Nr.1.1.1.1/16/A/182 on fundamental processes in phosphorescent materials has been published.

      V. Liepina, D. Millers * , K. Smits, A. Zolotarjovs, I. Bite

      SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. In this study we carried out the study of X-ray excited luminescence of SrAl2O4:Dy and SrAl2O4:Eu,Dy samples, including the measurements of afterglow at low temperatures within extended time scale. We observed both Eu and Dy luminescence peaks in the afterglow and TSL measurements. In recent articles the tunneling of electron from trap levels to excited Eu luminescence center was discussed, and in this research we conclude that under X-ray irradiation Eu2+ and Dy3+ serve as hole traps; electron tunneling is present in both SrAl2O4:Eu, Dy and SrAl2O4: Dy, and luminescence afterglow at 10 K arises from decay of excited Eu2+ and Dy3+ centers created via electron tunneling from host trap to Eu3+ and Dy4+ ions.

      Journal of Physics and Chemistry of Solids

      pdf-iconDownload PDF

      Teksta latviskotā versija pieejama šeit: http://www.lum.lv/rentgenstarojuma-ierosinata-sral2o4-luminescence-zemas-temperaturas/

      Project ERDF Project Nr.1.1.1.1/16/A/182: Phosphorescent coatings prepared by plasma electrolytic oxidation update

      PEO A certain project milestone has been recently achieved and luminescent coatings with sufficient luminescence intensity to be seen by the naked eye have been acquired. We will continue our work on intensity and luminescence afterglow parameter improvement and it certainly looks like we’re moving in the right direction although of course there’s tons of work still ahead of us.

      A publication studying optical properties of strontium aluminate has been submitted and is being reviewed.

      We’re also happy to announce that starting September Boriss Poļakovs and Krišjānis Auziņš have joined the project and are actively working to contribute to project’s successful ongoing.

      Improvements on PEO reactor chamber (see photo) have been  made to insure better repeatability and constant results, allowing to study the coatings with greater detail and less errors. Technical improvements have also been made to aluminum samples – it is now possible to split the samples into smaller pieces with absolutely no potential damage to the coating.

      Teksta latviskotā versija pieejama šeit. 

       

      PROMES CNRS visit

      Our team is visiting PROMES CNRS facilities (Font-Romeu, France). We are grateful for the access to the facilities in frame of SFERA 2 project. This great opportunity will be used to prepare samples for the successful realization of ERDF Project Nr.1.1.1.1/16/A/182.

      IMG-20170724-WA0000

      ERAF projekts -Fosforiscējoša pārklājuma iegūšana plazmas elektrolītiskajā oksidācijas procesā-.

      Līguma numurs 1.1.1.1/16/A/182

      Projekta ilgums: 27.02.2017 -31.10.2019

      Projekta zinātniskais vadītājs: Dr.phys. Krisjanis Smits

       

      Projekta mērķis ir ne-saimnieciskajā rūpnieciskajā pētījumā iegūt alumīniju saturošu fosforiscējošu pārklājumu plazmas elektrolītiskās oksidācijas (PEO) procesā.

      Projekta gaitā paredzēts PEO procesā iegūt leģētus ar Eu joniem aktivētus kompleksos oksīdus, izveidot aktivatoru nanokristālu pārklājumu poru aizpildīšanai un, veicot gala oksidāciju, PEO procesā iegūt luminiscentu pārklājumu. Paralēli veicamajām darbībām, tām tiks pielāgota SIA “ElGoo tech” īpašumā esošā PEO aparatūra un tās parametri, kā rezultātā iegūsim validētu nepatentētu tehnoloģiju. Tiks veikta iegūto materiālu īpašību (luminiscences, struktūras un morfoloģijas) izpēte. Plānots iepirkums, kura nolikumā, vērtēšanā un tehniskajā specifikācijā tiks piemēroti Zaļā publiskā iepirkuma kritēriji un principi.

      Ar saimniecisko darbību nesaistīto projektu plānots īstenot kopā ar sadarbības partneri – komersantu SIA “ElGoo tech” no 2017.gada 1.februāra līdz 2019.gada 31.oktobrim, ar kuru kopā ir izstrādāts šis projekts un noslēgts sadarbības līgums. Plānotās projekta izmaksas ir 539 844.50 EUR.

      Plānots iegūt 120 gab. fosforiscējoša pārklājuma paraugus, vienu šī procesa validētas nepatentētas tehnoloģijas aprakstu, 6 zinātniskos rakstus, piesaistīto privāto finansējumu un 1 komersantu, kurš sadarbojas ar pētniecības organizāciju. Pētījumā tiks nodarbināti vismaz 11 darbinieki, t.sk. 4, kuriem tiks izveidotas jaunas darba vietas.

      Projektu plānots īstenot inovatīvo materiālu un tehnoloģijas nozarē izmantojot starpdisciplinaritāti – dabas zinātnes (1.3 fizika (Physical sciences) un 1.4 ķīmija (Chemical sciences)) un inženierzinātnes un tehnoloģija (2.5 materiālu zinātne (Materials engineering) un 2.10 nanotehnoliģijas (Nano-technology)).

      Tiks pētīta iespēja izveidot luminiscentus pārklājumus, izmantojot plazmas elektroķīmisko oksidāciju (PEO). Patreiz PEO procesā iegūtie pārklājumi tiek aktīvi izmantoti, jo tiem piemīt labas aizsargājošās (liela cietība, laba nodilumizturība, termiskā aizsardzība, pretkorozijas uc.) īpašības. Metālu un dažu tā sakausējumu oksīdiem, ir labas optiskās īpašības, taču, piemēram, luminiscence PEO procesā iegūtiem pārklājumiem iepriekš nav pētīta. Pirmie pētījumi tika veikti SIA “ElGoo tech” sadarbojoties ar LU CFI, kuros iegūti pirmie labi luminiscējošie pārklājumi. Šie rezultāti un literatūrā atrodamie cita veida pētījumi parāda, ka ar PEO metodi iespējams izveidot arī fosforiscentos pārklājums, kuriem būtu ievērojams pielietojumu potenciāls, piemēram, SrAl2O4:Eu:Dy, kuram piemīt vienas no lielākajām kvantu efektivitātēm un ilgākā pēcspīdēšana.

      Tādēļ šī pētījumu projekta ietvaros plānots iegūt alumīniju saturošus pārklājumus ar ilgu pēcspīdēšanu (fosforiscenci). Iegūstamie pārklājumi būs caurspīdīgi tuvajā UV apgabalā, tādejādi gala pārklājumam būs vairākas reizes lielāka efektivitāte salīdzinot ar pārdošanā esošajām fosforiscentajām krāsām. vienlaicīgi fosforiscējošais pārklājums kalpos kā metālu atikorozijas pārklājums un šāda pārklājuma noturība, ilgmūžība būs daudz lielāka salīdzinot ar krāsām.

      Projekta sasniegtajiem rezultātiem pēc projekta beigām tiks nodrošināta:

      1. Finansiālā ilgtspēja – no valsts un privātā sektora budžeta tiks finansētas 4 jaunizveidotās darba vietas un finansēta projekta rezultātu publiskā pieejamība, SIA „ElGoo tech” no savas saimnieciskās darbības peļņas uzturēs projektā modificēto PEO aparatūru un budžetā paredzēs realizēt eksperimentālo pētījumu;
      2. Institucionālā ilgtspēja – 4 projektā iesaistītie zinātniskie darbinieki tiks nodarbināti jaunizveidotajās darba vietās, tā saglabājot pētījumā iegūto praktisko pieredzi un zinātību un izmantojot to tālākajā darbā, savukārt projekta īstenotāji (LU CFI un SIA „ElGoo tech”) apņemas pētījuma rezultātus izmantot savā turpmākajā zinātniskajā un saimnieciskajā darbībā;
      3. Politiskā ilgtspēja – ir nodrošināta, jo projekta mērķi atbilst RIS3 noteiktajiem tautsaimniecības transformācijas virzieniem un izaugsmes 1., 2. un 3.prioritātei. Projektu raksturojošie atslēgas vārdi – plazmas elektroķīmiskā oksidācija, pārklājumi, fosforiscence, luminiscence, oksīdi, nanokristāli.

       

      Oficiālā www.CFI.lv lapa par projektu ir atrodama šeit.

      Radioluminescence, thermoluminescence and dosimetric properties of ZnO ceramics

      Larisa Grigorjeva, Aleksejs Zolotarjovs, Sergej Yu Sokovnin, Donats Millers, Krisjanis Smits, Vladislav G. Il`ves

      Two types of ZnO ceramics were fabricated and characterized by XRD, SEM methods. The radioluminescence spectra were measured within the 300–550 K range. The defect luminescence band peaking at ~2.35 eV is the dominant one in radioluminescence spectra in both of the fabricated ceramics. The thermostimulated luminescence (TSL) glow-curves were measured after X-ray irradiation at 300 K. It was concluded that the complex overlapping peak within the 320–450 K temperature range consists of two components (~360–375 K and 400–420 K). The ratio of component intensities differs in both ceramics. The positions of high temperature TSL components (480–520 K) also differ in both samples; therefore not only sintering conditions but also the properties of the initial powder are very important for characteristics of TSL. A linear dependence of peak intensity on irradiation dose was observed up to ~3 kGy for ceramic 1 and up to 9 kGy for ceramic 2.

      cer_int_2017_img

      Ceramics International

      DOI: 10.1016/j.ceramint.2017.02.016

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      Effect of Mg2+ ions co-doping on luminescence and defects formation processes in Gd3(Ga,Al)5O12:Ce single crystals

      V. Babin , P. Bohacek , L. Grigorjeva , M. Kucera , M. Nikl , S. Zazubovich , A. Zolotarjovs
      Photo- and radioluminescence and thermally stimulated luminescence characteristics of Ce3+ – doped
      and Ce3+, Mg2+ co-doped Gd3(Ga,Al)5O12 (GAGG) single crystals of similar composition are investigated in the 9-500 K temperature range. The Ce3+ – related luminescence spectra and the photoluminescence decay kinetics in these crystals are found to be similar. Under photoexcitation in the Ce3+ – and Gd3+ – related absorption bands, no prominent rise of the photoluminescence intensity in time is observed neither in GAGG:Ce,Mg nor in GAGG:Ce crystals. The afterglow is strongly reduced in GAGG:Ce,Mg as compared to GAGG:Ce, and the afterglow decay kinetics is much faster. Co-doping with Mg2+ results in a drastic decrease of the thermally stimulated luminescence (TSL) intensity in the whole investigated temperature range and in the appearance of a new complex Mg2+ – related TSL glow curve peak around 285 K. After irradiation in the Ce3+ – related 3.6 eV absorption band, the TSL intensity in GAGG:Ce,Mg is found to be comparable with that in the GAGG:Ce epitaxial film of similar composition. The Mg2+ – induced changes in the concentration, origin and structure of the crystal lattice defects and their influence on the scintillation characteristics of GAGG:Ce,Mg are discussed.

       2017 gagg paper

      Optical Materials 66 (2017) 48-58

      DOI: 10.1016/j.optmat.2017.01.039

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      Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate

      Urmas Joost, Andris Šutka, Meeri Visnapuu, Aile Tamm, Meeri Lembinen, Mikk Antsov, Kathriin Utt, Krisjanis Smits, Ergo Nõmmiste and Vambola Kisand

      Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) smits 2017 imageand the film is
      made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

       

      Beilstein Journal of Nanotechnology

      Beilstein J. Nanotechnol. 2017, 8, 229–236.
      DOI:10.3762/bjnano.8.25

      The paper is open access. Download it from journal page here or by pressing the buttons below:

      pdf-icon Download PDF

       

      Tunneling luminescence in long lasting afterglow of SrAl2O4:Eu,Dy

      Virginija Liepina, Donats Millers, Krisjanis Smits

      A long lasting (afterglowing) luminescent material SrAl2O4: Eu2+, Dy3+ was prepared by high temperature solid-state reaction method. The processes responsible for long lasting luminescence were studied by means of luminescence spectra, thermally stimulated luminescence and afterglow kinetics.Two processes are found to contribute in excited Eu2+ creation – the thermally released electrons recombination and electron tunneling from trap to Eu3+. The possible scheme of long lasting luminescence mechanism is proposed.

      virginija raksts image.

      Journal of Luminescence

      http://dx.doi.org/10.1016/j.jlumin.2017.01.011

      DOI: 10.1016/j.jlumin.2017.01.011

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      Looking back. UPCON 2016: Bright future for upconversion

      A great review of the may-2016 conference that took place in Wroclaw, Poland!

      Check out the view from Dayong Jin published in Nature Photonics here.

      upcon_image

      Krisjanis Smits and Aleksejs Zolotarjovs had a really productive and interesting visit. We hope to meet again soon with all the participants of the conference.

      European Cooperation in Science and Technology (COST) Action CM1403

      Mechanical Reinforcement of Electrospun Poly(Vinyl Alcohol) by a-FeOOH Nanowires

      Anna Sutka, Martin Jarvekulg, Andris Sutka, Ivo Heinmaa, Uno Maeorg, Krisjanis Smits, Martin Timusk

      We report the mechanical performance of α-FeOOH nanowire reinforced poly(vinyl alcohol) (PVA) composite nanofiber mat, fabricated using straightforward aqueous processing methods. Goethite (α-FeOOH) nanocrystals have a high elastic modulus and –OH rich surface, ensuring strong interactions with hydrophilic polymers and effective reinforcement. Needle-less electrospinning resulted in alignment of the nanowires along fibre axis, as confirmed by transmittance electron microscopy studies. Produced composite PVA nanofibers containing 10 wt% goethite nanoparticles exhibited an outstanding fivefold increase in Young’s modulus and 2.5-fold improvement of tensile strength compared to mats of neat PVA. The addition of α-FeOOH had a significant influence on glass transition temperature indicating formation of interphase regions around nanowire inclusions. Observed properties are explained by nanowire grafting in the precursor solution, extensive interactions between the adsorbed PVA chains and the matrix and percolation of interphase regions at 10 wt% α-FeOOH.

      Published in Polymer Composites, John Wiley and Sons Ltd.

      DOI: 10.1002/pc.24231

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      Unexpected Epitaxial Growth of a Few WS2 Layers on 1100 Facets of ZnO Nanowires

      Boris Polyakov, Alexei Kuzmin, Krisjanis Smits, Janis Zideluns, Edgars Butanovs,
      Jelena Butikova, Sergei Vlassov, Sergei Piskunov, and Yuri F. Zhukovskii

      untitled-1

      Core-shell nanowires is an interesting and perspective class of radially heterostructured nanomaterials where epitaxial growth of the shell can be realized even at signi ficant core-shell lattice mismatch. In this study epitaxial hexagonally-shaped shell consisting of WS2 nanolayers was grown on f1100g facets of prismatic wurtzite-structured
      [0001]-oriented ZnO nanowires for the first time. A synthesis was performed by annealing in a sulfur atmosphere of ZnO/WO3 core-shell structures, produced by reactive
      DC magnetron sputtering of amorphous a-WO3 layer on top of ZnO nanowire array.
      The morphology and phase composition of synthesized ZnO/WS2 core-shell nanowires were con firmed by scanning and transmission electron microscopy (SEM and TEM),micro-Raman and photoluminescence spectroscopy. Epitaxial growth of WS2(0001) layer(s) on f1100g facets of ZnO nanowire is unexpected due to incompatibility of their symmetry and structure parameters. To relax the interfacial incoherence, we propose a model of ZnO/WS2 interface containing WS2 bridging groups inside and use first-principles simulations to support its feasibility.

      J. Phys. Chem. C

      DOI: 10.1021/acs.jpcc.6b06139

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      Luminescent PEO Coatings on Aluminum

      Aleksejs Zolotarjovs, Krisjanis Smits, Anete Krumina, DonatsMillers, and Larisa Grigorjeva

      Results show the possibilities of pore filling approach to modify alumina coatings with various materialspeo-raksta-bilde in order to enhance coating optical (or other) properties and develop new functional materials; as well as demonstrate novel alumina phase transition detection approach. Luminescent PEO coatings were
      produced on aluminum surface using pore-filling method. Three stage process was developed to modify alumina coating in order to enhance its luminescent properties. Eu3+ recharging to Eu2+ followed by significant (up to 10 times) total luminescence intensity increase was observed, Eu ion presence evaluated in final coating by measuring fast decay kinetics. Structure of obtained coatings was analyzed using XRD and FTIR spectroscopy indicating presence of η-alumina phase.

      ECS Journal of Solid State Science and Technology, 5 (9) R150-R153 (2016)

      DOI: 10.1149/2.0401609jss

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      Complex tribomechanical characterization of ZnO nanowires: nanomanipulations supported by FEM simulations

      Sergei Vlassov, Boris Polyakov, Sven Oras, Mikk Vahtrus,
      Mikk Antsov, Andris Šutka Krisjanis Smits, Leonid M Dorogin and
      Rünno Lõhmus

      Abstract
      In the present work, we demonstrate a novel approach to nanotribological measurements based
      on the bending manipulation of hexagonal ZnO nanowires (NWs) in an adjustable halfsuspended
      configuration inside a scanning electron microscope. A pick-and-place manipulation
      technique was used to control the length of the adhered part of each suspended NW. Static and
      kinetic friction were found by a ‘self-sensing’ approach based on the strain profile of the
      elastically bent NW during manipulation and its Young’s modulus, which was separately
      measured in a three-point bending test with an atomic force microscope. The calculation of static
      friction from the most bent state was completely reconsidered and a novel more realistic crackbased
      model was proposed. It was demonstrated that, in contrast to assumptions made in
      previously published models, interfacial stresses in statically bent NW are highly localized and
      interfacial strength is comparable to the bending strength of NW measured in respective bending
      tests.

      Nanotechnology 27 (2016) 335701 (10pp)

      doi:10.1088/0957-4484/27/33/335701

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      Europium(III)-doped A2Hf2O7 (A ¼ Y, Gd, Lu) nanoparticles: Influence of annealing temperature, europium(III) concentration and host cation on the luminescent properties

      Jelena Papan , Dragana J. Jovanovic , Katarina Vukovic , Krisjanis Smits ,
      Vesna ÐorCevic , Miroslav Dramicanin 

      The detailed analyses of structure and luminescence of europium(III)-doped A2Hf2O7 (A ¼ Y, Gd, Lu)
      nanoparticles is presented. Samples were prepared by time and cost effective combustion method that
      utilize polyethylene glycol both as a chelating agent and as a fuel, with different europium(III) concentrations
      (from 1 to 12 at.%), annealed at temperatures ranging from 800 to 1400 C, and with alternating
      A3þ cation in the A2Hf2O7 host. Then, structural variations between materials were analysed by Xray
      diffraction and structural refinement, while the changes in the luminescence were assessed from the
      Judd-Ofelt analyses of emission spectra. Nanoparticles prepared at the lowest temperature (800 C) had
      the smallest particle size of ~6 nm and showed the highest quantum efficiency when doped with 1 and
      2 at.% of europium(III). Radiative transition rate and quantum efficiency of emission showed
      Lu2Hf2O7 > Gd2Hf2O7 > Y2Hf2O7 trend.

      Optical Materials xxx (2016) 1e9

      doi:10.1016/j.optmat.2016.04.007

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      Effect of Point Defects on Luminescence Characteristics of ZnO Ceramics

      P. A. Rodnyi, K. A. Chernenko, A. Zolotarjovs, L. Grigorjeva,
      E. I. Gorokhova, and I. D. Venevtsev

      Abstract—Photo- and thermally stimulated luminescence of ZnO ceramics are produced by uniaxial hot pressing. The luminescence spectra of ceramics contain a wide band with a maximum at 500 nm, for which oxygen vacancies VO are responsible, and a narrow band with a maximum at 385 nm, which is of exciton nature. It follows from luminescence excitation spectra that the exciton energy is transferred to luminescence centers in ZnO. An analysis of the thermally stimulated luminescence curves allowed detection of a set of discrete levels of point defects with activation energies of 25, 45, 510, 590 meV, and defects with continuous energy distributions in the range of 50–100 meV. The parameters of some of the detected defects are characteristic of a lithium impurity and hydrogen centers. The photoluminescence kinetics are studied in a wide temperature range.
      DOI: 10.1134/S1063783416100309

      ISSN 1063-7834,

      Physics of the Solid State, 2016, Vol. 58, No. 10, pp. 2055–2061.

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      Ag sensitized TiO2 and NiFe2O4 three-component nanoheterostructures: synthesis, electronic structure and strongly enhanced visible light photocatalytic activity

      A. Šutka, T.
      Käämbre, R. Pärna, N. Doebelin, M. Vanags, K. Smits and V. Kisand

      This study reports on the synthesis and characterisation of two- and three-component visible light active photocatalytic
      nanoparticle heterostructures, based on TiO2 and NiFe2O4 and sensitized with Ag. We observe that Ag content as small as
      1 at.% in the TiO2/NiFe2O4 heterostructure increases by more than an order of magnitude the rate constant for the visible
      light photocatalytic process. We rationalise this in terms of the measured structure and electronic structure data of the
      binary and ternary combinations of the component materials and focus on details, which show that an optimised
      deposition sequence is vital for attaining the high values of photocatalytic efficiency, because the charge transfer across
      the interfaces appears to be sensitive to where the Ag is loaded in the heterostructure. The overall higher visible light
      photocatalytic activity of the TiO2/Ag/NiFe2O4 heterostructure was observed and is attributed to enhanced charge carrier
      separation efficiency and migration via vectorial electron transfer.

      RSC Advances., 2016,

      DOI: 10.1039/C6RA00728G

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      Rare earth doped glass–ceramics containing NaLaF4 nanocrystals

      E. Elsts , G. Krieke, U. Rogulis, K. Smits, A. Zolotarjovs, J. Jansons, A. Sarakovskis, K. Kundzins

      Oxyfluoride glasses 16Na2O–9NaF–5LaF3–7Al2O3–63SiO2 (mol%) activated with 3% terbium, dysprosium,
      praseodymium and neodymium fluorides have been prepared and studied by differential thermal analysis,
      cathodoluminescence, X-ray induced luminescence, X-ray diffraction, scanning electron microscopy
      and energy dispersive X-ray spectroscopy. We found out that the presence of crystalline phase enhances
      the X-ray induced luminescence intensity. X-ray induced luminescence is the most intense for the sample
      activated with terbium and treated at 700 C, whereas the praseodymium and neodymium activated
      samples have the fastest decay times.

      Optical Materials xxx (2016) xxx–xxx

      doi: 10.1016/j.optmat.2016.01.005

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      Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond

      A. Jarmola, A. Berzins, J. Smits, K. Smits, J. Prikulis, F. Gahbauer, R. Ferber, D. Erts, M. Auzinsh, and D.
      Budker

      We present systematic measurements of longitudinal relaxation rates (1=T1) of spin polarization in
      the ground state of the nitrogen-vacancy (NV–) color center in synthetic diamond as a function
      of NV– concentration and magnetic field B. NV– centers were created by irradiating a Type 1b
      single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron
      microscope with varying doses to achieve spots of different NV– center concentrations. Values of
      (1=T1) were measured for each spot as a function of B

      Applied Physics Letters 107, 242403 (2015);

      doi: 10.1063/1.4937489

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      Luminescence of polymorphous SiO2

      A.N. Trukhin, K. Smits, J. Jansons, A. Kuzmin

      The luminescence of self-trapped exciton (STE) was found and systematically studied in tetrahedron
      structured silica crystals (a-quartz, coesite, cristobalite) and glass. In octahedron structured stishovite
      only host material defect luminescence was observed. It strongly resembles luminescence of oxygen
      deficient silica glass and g or neutron irradiated a-quartz. The energetic yield of STE luminescence for aquartz
      and coesite is about 20% of absorbed energy and about 5(7)% for cristobalite. Two types of STE
      were found in a-quartz. Two overlapping bands of STEs are located at 2.5e2.7 eV. The model of STE is
      proposed as SieO bond rupture, relaxation of created non-bridging oxygen (NBO) with foundation of a
      bond with bridging oxygen (BO) on opposite side of c or x,y channel. The strength of this bond is
      responsible for thermal stability of STE. Similar model of STE was ascribed for coesite and cristobalite
      with difference related to different structure. STE of Silica glass is strongly affected by disordered
      structure.

      Radiation Measurements 90 (2016) 6e13

      doi:10.1016/j.radmeas.2015.12.002

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      Multicolor upconversion luminescence of GdVO4:Ln3þ/Yb3þ (Ln3þ ¼ Ho3þ, Er3þ, Tm3þ, Ho3þ/Er3þ/Tm3þ) nanorods

      Tamara V. Gavrilovic , Dragana J. Jovanovic,  Krisjanis Smits, Miroslav D. Dramicanin 

      Lanthanide-doped GdVO4 nanorods that exhibit upconversion emission under 982 nm excitation have
      been prepared by a facile room-temperature chemical co-precipitation method followed by a subsequent
      annealing at temperatures of 600 C, 800 C and 1000 C. Multicolor upconversion emission, including
      white, was achieved by tuning the concentrations of dopant lanthanide ions (Ho3þ, Er3þ, Tm3þ and Yb3þ)
      in GdVO4. It is found that four GdVO4 samples emit light with the white chromaticity coordinates of
      (0.326, 0.339), (0.346, 0.343), (0.323, 0.327) and (0.342, 0.340) respectively, under a single-wavelength
      NIR excitation. These coordinates are very close to the standard equal energy white light coordinates
      (0.333, 0.333) according to the 1931 CIE diagram. By varying dopant lanthanide concentrations in
      nanorods it is possible to produce upconversion emission with colors between red (0.504, 0.369), green
      (0.282, 0.577) and blue (0.142, 0.125) coordinates.

      Dyes and Pigments 126 (2016) 1e7

      doi:10.1016/j.dyepig.2015.11.005

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      Gas sensitive luminescence of ZnO coatings obtained by plazmaelectrolytic oxidation

      L. Grigorjeva, D. Millers, K. Smits, A. Zolotarjovs

      The ZnO coatings on Zn substrate were obtained using plasma electrolytic oxidation method. The XRDand SEM methods were used for structural and morphological characterization of obtained coatings. Theluminescence of ZnO coatings were studied and compared with luminescence characteristics of ZnO sin-gle crystal. It is shown that luminescence intensity in ZnO defect band depends on oxygen concentrationin ambient atmosphere. The effect is of interest for oxygen sensing based on ZnO coating luminescence

      Sensors and Actuators A 234 (2015) 290–293

      doi:10.1016/j.sna.2015.09.018

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