Projekta ERAF Projekts Nr.126.96.36.199/16/A/182 ietvaros publicēts jauns raksts par fundamentāliem procesiem fosforescentos materiālos.
Projekta ERAF Projekts Nr.188.8.131.52/16/A/182 ietvaros publicēts jauns raksts par fundamentāliem procesiem fosforescentos materiālos.
Successful meeting with colleagues from Germany and Russia. Discussing the last stages of ERANET RUS project ending this year.
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.
Published in Particle & Particle Systems Characterization.
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.
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
ZnO ceramics and dosimetry!
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.
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.
Optical Materials 66 (2017) 48-58
Great work! Krisjanis Smits took his part in this unique research.
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) and 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.
The paper is open access. Download it from journal page here or by pressing the buttons below:
Starting the year with strontium aluminates! Great work by the members of the laboratory! Take a look!
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.
Journal of Luminescence
A great review of the may-2016 conference that took place in Wroclaw, Poland!
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.
PhD.phys. student Aleksejs Zolotarjovs and M.Sc. student Katrīna Laganovska both received the grant for Students and Young scientists.
Successful discussion concerning further steps in our international ERANET RUS PLUS, NanoRadDos project! Thanks to our colleagues in Cologne for great organisation of the event!
Our student Aleksejs Zolotarjovs just presented his ISSP young researchers project proposal about functional PEO coatings:
Our article was advertised on the front cover of Nanotechnology journal.
Pleasant surprise! Sergei Vlassov! It was interesting to participate in this research.
Boris Polyakov, Alexei Kuzmin, Krisjanis Smits, Janis Zideluns, Edgars Butanovs,
Jelena Butikova, Sergei Vlassov, Sergei Piskunov, and Yuri F. Zhukovskii
Core-shell nanowires is an interesting and perspective class of radially heterostructured nanomaterials where epitaxial growth of the shell can be realized even at significant core-shell lattice mismatch. In this study epitaxial hexagonally-shaped shell consisting of WS2 nanolayers was grown on f1100g facets of prismatic wurtzite-structured
-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 confirmed 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
Aleksejs Zolotarjovs, Krisjanis Smits, Anete Krumina, DonatsMillers, and Larisa Grigorjeva
Results show the possibilities of pore filling approach to modify alumina coatings with various materials 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)
Sergei Vlassov, Boris Polyakov, Sven Oras, Mikk Vahtrus,
Mikk Antsov, Andris Šutka Krisjanis Smits, Leonid M Dorogin and
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
Nanotechnology 27 (2016) 335701 (10pp)
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
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.
Physics of the Solid State, 2016, Vol. 58, No. 10, pp. 2055–2061.
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,
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
A. Jarmola, A. Berzins, J. Smits, K. Smits, J. Prikulis, F. Gahbauer, R. Ferber, D. Erts, M. Auzinsh, and D.
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  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);
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
Radiation Measurements 90 (2016) 6e13
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
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