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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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


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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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Studies of radiation defects in cerium, europium and terbium activated oxyfluoride glasses and glass ceramics

E. Elsts , U. Rogulis, K. Bulindzs, K. Smits, A. Zolotarjovs, L. Trinkler, K. Kundzins

Terbium, cerium and europium activated oxyfluoride glasses and glass ceramics have been studied by
thermally stimulated luminescence (TSL) and optical absorption techniques after the X-ray irradiation.
A creation of colour centres in oxyfluoride glass matrix and TSL peaks depending on the activator type
were observed. LaF3 and rare earth activators were analysed by SEM–EDS.

Optical Materials 41 (2015) 90–93

DOI: 10.1016/j.optmat.2014.10.042

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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 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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Up-conversion luminescence dependence on structure in zirconia nanocrystals

Krisjanis Smits, Dzidra Jankovica , Anatolijs Sarakovskis, Donats Millers

The zirconia samples containing two different concentrations of Er and Yb dopants were prepared using
the Sol–Gel method and up-conversion luminescence was studied using the time-resolved techniques.
The up-conversion luminescence depends on the oxygen content in surrounding gasses during annealing
as well as on the annealing temperature. These dependencies indicate that ZrO2 intrinsic defects annealing
and generation, phase transition as well as dopant redistribution take place. The possible role of these
processes on up-conversion luminescence is discussed. The results of experiments confirmed that the
annealing temperature has a crucial influence on up-conversion luminescence for samples containing
small concentrations of Er and Yb; whereas for samples containing large concentrations of Er and Yb,
the primary change of up-conversion luminescence is due to the grain size growth during annealing.
The optimal annealing temperature depends upon the Er and Yb ion concentration. It is crucial to obtain
up-conversion zirconia material with high quantum efficiency.

Optical Materials 35 (2013) 462–466

DOI: 10.1016/j.optmat.2012.09.038

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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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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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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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