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.


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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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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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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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


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Luminescence of Er/Yb and Tm/Yb doped FAp nanoparticles and ceramics

L. Grigorjeva, K. Smits, D.Millers, Dz.Jankoviča

Abstract. The nanoparticles of hydroxiapatite and fluorapatite doped with
Er/Yb and Tm/Yb were synthesized and characterized by FTIR, XRD, SEM and
TEM methods. The results of up-conversion luminescence studies were
presented for the samples as prepared, annealed at 500°C and at 900-1000 °C.
At annealing above 800°C the ceramic state was formed. It is shown that
fluorapatite host is more appropriate than hydroxiapatite host for rare ions
luminescence and up-conversion processes. The post preparing annealing of
nanarticles significantly enhanced the luminescence intensity. The Tm/Yb
doped fluorapatite shows intense up-conversion luminescence in 790-800 nm
spectral region and is potentially useful for biomedical applications.

IOP Conference Series: Materials Science and Engineering 77 (2015) 012036


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Thermally stimulated luminescence of undoped and Ce3+-doped Gd2SiO5 and (Lu,Gd)2SiO5 single crystals

V. Bondar, L. Grigorjeva, T. Kärner, O. Sidletskiy,
K. Smits, S. Zazubovich, A. Zolotarjovs

Thermally stimulated luminescence (TSL) characteristics (TSL glow curves and TSL
spectra) are investigated in the 4-520 K temperature range for the X-ray irradiated at 4 K, 8
K, or 80 K single crystals of gadolinium and lutetium-gadolinium oxyorthosilicates. The
nominally undoped Gd2SiO5 and (Lu,Gd)2SiO5 crystals, containing traces of Ce3+, Tb3+, and
Eu3+ ions, and Ce3+-doped Gd2SiO5 and (Lu,Gd)2SiO5 crystals are studied. For the first time,
the TSL glow curves of these materials are measured separately for the electron (intrinsic,
Ce3+- or Tb3+-related) and hole (Eu3+-related) recombination luminescence, and the TSL glow
curve peaks, arising from thermal decay of various electron and hole centers, are identified.
The origin of the traps related to the TSL peaks is discussed, and thermal stability parameters
of the electron and hole traps are calculated.

Journal of Luminescence


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Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition

Krisjanis Smits , Larisa Grigorjeva , Donats Millers , Karlis Kundzins , Reinis Ignatans , Janis Grabis , Claude Monty

Zirconia nanocrystals have attracted considerable interest as biolabels, which can be used as probes for
medical imaging and biosensor applications. However, zirconia particle agglomeration forms amajor limitation
to its use for biolabeling. In this backdrop, for the first time, well-separated zirconia nanocrystals
were obtained in a Heliotron reactor (PROMES CNRS, France) via the solar physical vapor deposition
(SPVD) method. As the raw material target for solar evaporation, zirconia nanopowders obtained via
the sol–gel process were used. The luminescence and upconversion luminescence properties of the Sol
Gel nanopowders were compared with those of the SPVD nanocrystals. Erbium was chosen as the luminescence
center with ytterbium as the sensitizer, and along with these two dopants, niobium was also
used. Niobium acts as a charge compensator to compensate for depletion in the charge due to the
introduction of trivalent erbium and ytterbium at tetravalent zirconium sites. Consequently, the
oxygen-vacancy concentration is reduced, and this results in a significant increase in the upconversion
The SPVD-prepared samples showed less agglomeration and a fine crystal structure as well as high
luminescence, and thus, such samples can be of great interest for biolabeling applications.

Optical Materials 37 (2014) 251–256

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The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

K. Smits, A. Sarakovskis, L. Grigorjeva, D. Millers, and J. Grabis

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity
in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb
co-doping were prepared by sol-gel method and thermally annealed to check for the impact of
phase transition on luminescence properties. Phase composition and grain sizes were examined by
X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission
electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison
of samples with different oxygen vacancy concentrations and different Nb concentrations
confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic
phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they
also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain
surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion
luminescence intensity. Hence, ZrO2:Er:Yb:Nb nanocrystals may show promise for upconversion

Journal of Applied Physics 115, 213520 (2014)


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The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

K. Smits, A. Sarakovskis, L. Grigorjeva, D. Millers, J. Grabis

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity
in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb
co-doping were prepared by sol-gel method and thermally annealed to check for the impact of
phase transition on luminescence properties. Phase composition and grain sizes were examined by
X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission
electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison
of samples with different oxygen vacancy concentrations and different Nb concentrations
confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic
phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they
also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain
surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion
luminescence intensity. Hence, ZrO2:Er:Yb:Nb nanocrystals may show promise for upconversion

VC 2014 AIP Publishing LLC.

doi: 10.1063/1.4882262

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Photocatalytic Properties of TiO2 and ZnO Nanopowders

L. Grigorjeva, J. Rikveilis, J. Grabis, Dz. Jankovica,
C. Monty, D. Millers, K. Smits

Photocatalytic activity of TiO2 and ZnO nanopowders is studied
depending on the morphology, grain sizes and method of synthesizing.
Photocatalysis of the prepared powders was evaluated by degradation of the
methylene blue aqueous solution. Absorbance spectra (190–100 nm) were
measured during exposure of the solution to UV light. The relationships
between the photocatalytic activity and the particle size, crystal polymorph
phases and grain morphology were analyzed. The photocatalytic activity of
prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile
phase ratio. Comparison is given for the photocatalytic activity of ZnO
nanopowders prepared by sol-gel and solar physical vapour deposition
(SPVD) methods

Latvian Journal of Physics and Technical Sciences 2013, N 4

DOI: 10.2478/lpts-2013-0025

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Characterization of hydroxyapatite by time-resolved luminescence and FTIR spectroscopy

L.Grigorjeva, D.Millers, K.Smits, Dz.Jankovica, L.Pukina

Abstract. Time-resolved luminescence and FTIR absorption spectra of undoped and Eu
and Ce doped hydroxyapatite nanocrystalline powders prepared by sol-gel method were
studied. The luminescence band at 350-400 nm was detected and two decay times (11 ns
and 38 ns) was determinated for Ce doped samples. The luminescence spectra and decay
kinetics were analized for Eu doped nanopowders. The Eu3+ ion was incorporated in
different Ca sites. The process of energy transfer to Eu3+ excited state (5D0) was detected
from luminescence decay kinetics.

IOP Conference Series: Materials Science and Engineering 49 (2013) 012005


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The electron beam induced short lived absorption in PLZT optical ceramics

D. Millers , V. Dimza, L. Grigorjeva, M. Antonova, K. Smits, M. Livins

The short lived absorption induced by a pulsed electron beam in the led–lanthanum–zirconate–titanate
(PLZT) optical ceramics was studied. The measured absorption spectrum covers 1.1–2.9 eV energy range
and consists of several strongly overlapping peaks. The rise of the absorption is delayed with respect to
the excitation pulse, due to charge carrier migration before trapping at centers responsible for the
absorption. The formation rate of absorption centers and decay rate of absorption depend on the photon
energy. The kinetics of short lived absorption varies over spectrum and can be approximated with a
stretched exponent. The stretched exponent parameters indicate that the local disorder of a matrix is
similar around all absorption centers.

Optical Materials xxx (2013) xxx–xxx

DOI 10.1016/j.optmat.2012.12.029

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Nanocomposites for Novel Sensing Systems

A. Sternberg, I. Muzikante, R. Dobulans, D. Millers, L. Grigorjeva, K. Smits, M. Knite, and G. Sakale

Abstract The work performed under the National Research Program of Latvia
and presented here is about advanced, chemical stimuli responsive materials.
Sensor materials are produced on the basis of metallophthalocyanines or zirconia
nanocrystals with the purpose of detecting small size molecular compounds like
NH3, O2 and O3. Polymer/nanostructured carbon composite is produced to detect
large size molecular compounds like organic vapour. Basic gaseous compound
sensing principles are discussed within this paper.

Physics and Biophysics

DOI 10.1007/978-94-007-4119-5_12

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The luminescent properties of persistent strontium aluminate phosphor prepared by solar induced solid state synthesis

V Liepina, K Smits, D Millers, L Grigorjeva, C Monty

Abstract. A novel method – solar induced solid state synthesis – for the synthesis of aluminate phosphor doped with Eu and Dy and the study of its luminescent properties are presented in this article. Two kinds of samples of persistent strontium aluminate phosphor have been prepared – ones via this new method and ones via conventional high temperature solid state reaction. Both kinds of samples were made using the same raw materials. The samples were tested for their chemical composition using X-Ray diffraction method. The luminescence properties and phase composition of the obtained samples have been compared. The behaviour of afterglow, thermally stimulated luminescence, excitation and emission spectra are presented.

IOP Conference Series: Materials Science and Engineering 38 (2012) 012045


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The time-resolved luminescence characteristics of Ce and Ce/Pr doped YAG ceramics obtained by high pressure technique

L. Grigorjeva , D. Millers , K. Smits , A. Sarakovskis , W. Lojkowski , A. Swiderska-Sroda , W. Strek ,
P. Gluchowski

Transparent Ce and Ce/Pr doped YAG ceramics were prepared under high pressures (up to 8 GPa) and relative
low temperature (450 C). Grain size of the ceramics is less than 50 nm. However unknown defects
or disorders strains on grain boundaries caused the additional absorption in these ceramics. The luminescence
intensity, spectra and the decay time dependence on pressure applied during ceramic preparation
were studied. Concentration of some intrinsic point defect was reduced under the high pressure applied
for sintering process.
It is shown that formation time of the excited state of Ce luminescence depends on the pressure applied
during ceramic sintering.

Optical Materials 34 (2012) 986–989


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Defect Luminescence of YAG Nanopowders and Crystals

L. Grigorjeva, D. Jankoviča, K. Smits, D. Millers, S. Zazubovich

Undoped and rare-earth-ion-doped Y3Al5O12 (YAG) nanopowders are prepared by the sol-gel low-temperature combustion method. The luminescence characteristics of the YAG, YAG:Ce, YAG:Pr, and YAG:Ce/Pr nanopowders are compared with those of the single crystals. The luminescence band peaking around 3.1 eV is complex and excited at about 3.6 eV, 3.9 eV and 4.3 eV. The 3.1 eV emission was peculiar to all the samples studied. The Stokes shift of this band is ~0.5 eV. The decay time of the ~3.1 eV emission at 80 K is ~14 ns and the slower decay (afterglow) components are practically absent. The 3.1 eV luminescence was suggested to arise from different intrinsic lattice defects.

Latvian Journal of Physics and Technical Sciences 2012, N 4

DOI: 10.2478/v10047-012-0022-4

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Intrinsic defect related luminescence in ZrO2

K. Smits , L. Grigorjeva , D. Millers, A. Sarakovskis, J. Grabis, W. Lojkowski

The studies of ZrO2 and yttrium stabilized ZrO2 nanocrystals luminescence as well as yttrium stabilized
single crystal luminescence and induced absorption showed that the intrinsic defects are responsible
for luminescence at room temperature. These defects form a quasi-continuum of states in ZrO2 band
gap and are the origin of the luminescence spectrum dependence on the excitation energy.
Luminescence centers are oxygen vacancies related but not the vacancies themselves. At room
temperature, in ZrO2, deep traps for electrons and holes exist. The oxygen vacancies are proposed to
be the traps for electrons.

Journal of Luminescence 131 (2011) 2058–2062


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Europium doped zirconia luminescence

Krisjanis Smits , Larisa Grigorjeva a, Donats Millers , Anatolijs Sarakovskis , Agnieszka Opalinska ,
Janusz D. Fidelus , Witold Lojkowski 

The luminescence properties and crystalline structure of ZrO2:Eu nanocrystals doped with different concentrations
of Eu were studied. Luminescence from the Eu2+ state was not observed even if the electrons
and holes were created up to 1019 cm3; thus it was suggested the Eu3+ was not an efficient trap for
electrons possibly due to Eu3+ negative charge relative to the crystalline lattice. The mutual interaction
between Eu3+ ions was not strong up to 5 at.% concentration. The stabilization of ZrO2 tetragonal as well
as cubic structure by Eu3+ is possible.

Optical Materials 32 (2010) 827–831


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The luminescence of ZnO ceramics

L. Grigorjeva , D.Millers , K.Smits , J.Grabis , J.Fidelus , W. qojkowski , T.Chudoba , K.Bienkowski 

The luminescence properties of ZnO ceramics with grains 100-5000 nm sintered by different techniques from nanopowders were studied. The luminescence decay times were compared with that obtained for ZnO singlecrystal. The temperature dependence of non-exponential decay of defect luminescence (2.0-2.6 eV) was measured in wide time, intensity and temperature range.The luminescence decay kinetic at T=20 K shows the decay close to I(t) w t1 dependence. At temperature region 50-250 K the decay kinetics is more complicated since the TSL was observed in this temperature region. It is shown that the luminescence properties of NP and ceramics strongly depend on defect distribution on grains surface
and the volume/surface ratio determine the luminescence decay in ZnO nanostructures and ceramics.

Radiation Measurements


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Time-resolved cathodoluminescence and photoluminescence of nanoscale oxides

L. Grigorjeva, D. Millers, A. Kalinko, V. Pankratov, K. Smits

The nanostructured oxide materials such as ZnO, ZrO2, and Y3Al5O12 (YAG) are perspective materials for transparent scintillating and/or
laser ceramics. The luminescence properties of single crystals, nanopowders and ceramic were compared. Nominally pure and rare-earth doped
nanopowders and ceramics have been studied by means of time-resolved luminescence spectroscopy.
The fast blue luminescence band was studied in ZnO ceramics sintering from different raw materials.
The luminescence centres of ZrO2:Y were compared in a single crystal, ceramic and nanopowder.
It is shown that ceramic sintering parameters have a strong influence on time-resolved luminescence characteristics in cerium-doped YAG.

Journal of The European Ceramic Society


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Advanced nanocrystalline ZrO2 for optical oxygen sensors

Janusz D. Fidelus and Witold Łojkowski, Donats Millers, Krisjanis Smits and Larisa Grigorjeva

Abstract It was shown that ZrO2 nanopowders and
nanoceramics can be used as an optical oxygen sensor,
where the luminescence signal is proportional to the
partial oxygen pressure in gases. The nanopowders were
obtained in a hydrothermal microwave driven process
followed by annealing at 750oC. Nanoceramics were
obtained by sintering at pressures up to 6 GPa and at
250oC so that grain growth did not occur. Luminescence
of both materials depends linearly on the oxygen content
in nitrogen-oxygen mixtures for 2.1% – 25 vol% oxygen
content. For luminescence excitation using a laser beam,
the luminescence intensity decreases as oxygen pressure
increases. For excitation with an electron beam, the
opposite effect is observed – the lower the oxygen
pressure, the lower the luminescence signal. The
experimental results are explained in terms of
luminescence centers being distorted lattice sites close to

Proceedings of IEEE Sensors 2009

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Excitonic luminescence in ZnO nanopowders and ceramics

L. Grigorjeva , D. Millers , K. Smits , V. Pankratov , W. Łojkowski, J. Fidelus , T. Chudoba , K. Bienkowski , C. Monty 

Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were
studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders
by high pressure (8 GPa) and low temperature (350 C). Ceramics with grain sizes 1–5 lm were sintered
at 1400 C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing
annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow
at 30 ns was 0.05%.

Optical Materials 2009


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Time-resolved absorption and luminescence following electron-hole pair creation in ZnO

R. Andrew Wall, Kyle C. Lipke, K. B. Ucer, R. T. Williams, D. Millers, K. Smits, and L. Grigorjeva

We report transient absorption induced by electron-hole excitation
in undoped ZnO. A laser pump/continuum probe
method covers 2–300 ps, and an electron pulse with lamp
transmission covers 8–300 ns. The broad absorption spectrum
increases monotonically with wavelength from 900 to 1600
nm. Following a reasonable hypothesis that the free-carrierlike
induced infrared absorption is proportional to the total
number of free carriers, excitons, and shallow-trapped carriers
in the sample, these data allow setting an upper limit on
the quantum efficiency of a specified lifetime component of
luminescence. For the undoped commercial ZnO studied in
this report, the quantum efficiency of room temperature excitonic
luminescence is less than 5%. This means that there is
significant room for improvement in applications aiming to
use room-temperature excitonic blue luminescence of ZnO
for fast scintillators and light sources. Direct observation that
a large majority of excitations are tied up for more than 100
nanoseconds in shallow traps confirms the premise for studies
undertaken at Oak Ridge National Laboratory to improve the
excitonic luminescence yield and decay rate of ZnO by donor
doping. The preliminary results presented here on undoped
ZnO suggest that induced absorption measurements should be
a useful diagnostic of quantum efficiency while studying such
dopant effects.

Physica Status Solidi (C) Current Topics in Solid State Physics

DOI 10.1002/pssc.200879896

phys. stat. sol. (c) 6, No. 1, 323–326 (2009)

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Radiative Decay of Electronic Excitations in ZrO Nanocrystals and Macroscopic Single Crystals

Krisjanis Smits, Larisa Grigorjeva, Donats Millers, Janusz D. Fidelus, and Witold Lojkowski

Abstract—The time-resolved luminescence was studied for
ZrO:Y single crystal and nanocrystals. The similar recombination
centres were found in both—single crystal and nanocrystals.
Luminescence decay is within 200 ns in nanocrystals, whereas it
extends to the microseconds in single crystal. It was shown that
the defects responsible for transient absorption were not involved
directly in radiative recombination process.

IEEE Transactions on Nuclear Science, VOL. 55, NO. 3, JUNE 2008

Digital Object Identifier 10.1109/TNS.2008.924077

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Luminescence Properties of ZnO Nanocrystals and Ceramics

Larisa Grigorjeva, Donats Millers, Janis Grabis, Claude Monty, Aleksandr Kalinko, Krishjanis Smits,
Vladimir Pankratov, and Witold Łojkowski

Abstract—The luminescence excitation spectra, luminescence
spectra and the nanosecond-scale decay kinetics were studied.
The ZnO and ZnO:Al nanopowders were prepared by vaporization-
condensation in a solar furnace using different raw powders:
commercial, hydrothermal and those obtained by plasma synthesis.
Exciton-phonon as well as exciton-exciton interaction
processes in nanopowders, a bulk crystal and ZnO ceramics were
studied and compared. The fast decay and low afterglow intensity
of ZnO nanopowders and ceramics support these materials for

IEEE Transactions on Nuclear Science, VOL. 55, NO. 3, JUNE 2008

Digital Object Identifier 10.1109/TNS.2008.921931

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Transient and stable color centers in neutron irradiated MgO

Vera Skvortsova, Nina Mironova-Ulmane, Larisa Grigorjeva,
Donats Millers, Krisjanis Smits

The transient absorption and luminescence induced by the pulsed electron beam have been investigated in the MgO single crystal
containing transition metal ion (Cr, Mn, Fe) impurities and preliminary irradiated by the fast neutrons. It is supposed that the different
behavior of the absorption spectra of the MgO samples preliminary irradiated by the different fast neutron fluence is connected with the
destruction of the hole centers and with the creation of interstitial protons and the formation of the microphase Mg(OH)2. We assume
that the luminescence band at 3.2 eV is connected with F+ color centers.

Nuclear Instruments and Methods in Physics Research B 266 (2008) 2941–2944


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Zirconia Based Nanomaterials for Oxygen Sensors – Generation, Characterisation and Optical Properties

Janusz D. Fidelus, Witold Lojkowski, Donats Millers,
Larisa Grigorjeva, Krishjanis Smits and Robert R. Piticescu

Abstract: Microwave driven hydrothermal synthesis and hydrothermal synthesis were used to
obtain ZrO2 nanopowders. Their production with varying phase composition, the characterisation
and selected optical properties concerning their potential use as luminescence oxygen sensors are
reported. It was found that the powders obtained by the microwave driven hydrothermal method
and annealed at 750 0C in air show experiment repeatability within an accuracy of 6 %.

Solid State Phenomena Vol. 128 (2007) pp. 141-150

© (2007) Trans Tech Publications, Switzerland

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Comparison of ZrO2:Y Nanocrystals and Macroscopic Single Crystal Luminescence

Krisjanis Smits, Donats Millers, Larisa Grigorjeva, Janusz D. Fidelus, Witold Lojkowski

Abstract. The luminescence spectra of a tetragonally structured ZrO2:Y single crystal and
nanocrystals were compared. It was found that the number of luminescence centers contributed
to the spectra. The excitation of luminescence within the band gap region led to different
luminescence spectra for the single crystal and nanocrystal samples, whereas recombinative
luminescence spectra were the same for both samples. The origin of this difference is that in
the nanocrystals, even under excitation within the band gap, charge carriers were created.
Zirconium- oxygen complexes distorted by intrinsic defects were proposed to be the
luminescence centres responsible for the wide luminescence band observed.

Journal of Physics: Conference Series 93 (2007) 012035


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The Luminescence Properties of ZnO nanopowders

Aleksandr Kalinko, Janusz D. Fidelus, Larisa Grigorjeva, Donats Millers, Claude J. Monty, Adam Presz and Krisjanis Smits

Abstract. Pure and Al3+ doped ZnO nanopowders were studied by means of time-resolved
luminescence spectroscopy. The powders were synthesized by hydrothermal and plasma
methods. These powders were used as a raw material for vaporization-condensation process
inside the Solar reactor. The commercially available ZnO nanopowder was studied for a
comparison. Exciton to defect band luminescence intensity ratio was estimated in different
types of ZnO nanopowders. It was found that nanopowders with whiskers morphology show
superlinear luminescence intensity depending on excitation density. The observed effect
depends on the average nanoparticle size and on the powder morphology.

IOP Publishing
Journal of Physics: Conference Series 93 (2007) 012044


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The Luminescence Properties of ZnO:Al Nanopowders Obtained by Sol-gel, Plasma and Vaporization-condensation Methods

Larisa Grigorjeva, Donats Millers, Krishjanis Smits, Claude Monty, Jules Kouam and Lassad El Mir

Abstract: ZnO nanocrystals were synthesized and characterized by XRD and SEM methods. The
luminescence spectra and decay kinetics were studied under pulsed laser excitation (266 nm, 8 ns).
ZnO and ZnO:Al powders were prepared by sol-gel and plasma chemical synthesis. These powders
were used as a raw material for the SPVD (Solar Physical Vapour Deposition) process. In this way,
the vaporisation-condensation phenomenon (VC) led to the formation of ZnO whiskers and
nanopowders. The luminescence properties of the VC nanopowders were studied and compared to
those displayed by the raw material. The Al dopant, present in the raw powders as a solid solution
and ZnAl2O4 precipitates, was only present as Al ions in the nanopowders after the SPVD. The blue
luminescence intensity increased considerably after SPVD. The whiskers type microstructures
showed nonlinear blue luminescence dependent on the excitation pulse density.

Solid State Phenomena 2007 Continue reading “The Luminescence Properties of ZnO:Al Nanopowders Obtained by Sol-gel, Plasma and Vaporization-condensation Methods”

Luminescence of oxygen related defects in zirconia nanocrystals

K. Smits, L. Grigorjeva, W. Łojkowski, and J. D. Fidelus

The luminescence of undoped tetragonal structure ZrO2 nanocrystals was studied. The luminescence intensity
depends on oxygen content in gases mixture in which the nanocrystals were annealed. The distorted
Zr-O bond is suggested to be the recombination center for band carriers. The oxygen deficient defect
is proposed to be responsible for photoluminescence.

Physica Status Solidi (C) Current Topics in Solid State Physics 4, No. 3, 770– 773 (2007)

DOI 10.1002/pssc.200673850

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