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
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
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
K Smits, J Liepins, M Gavare, A Patmalnieks, A Gruduls and D Jankovica
Abstract. Inorganic nanocrystals are of increasing interest for their usage in biology and pharmacology research. Our interest was to justify ZrO2 nanocrystal usage as submicron level biological label in baker’s yeast Saccharomyces cerevisia culture. For the first time (to our knowledge) images with sub micro up-conversion luminescent particles in biologic media were made. A set of undoped as well as Er and Yb doped ZrO2 samples at different concentrations were prepared by sol-gel method. The up-conversion luminescence for free standing and for nanocrystals with baker’s yeast cells was studied and the differences in up-conversion luminescence spectra were analyzed. In vivo toxic effects of ZrO2 nanocrystals were tested by co-cultivation with baker’s yeast.
IOP Conference Series: Materials Science and Engineering 38 (2012) 012050
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
L. Grigorjeva , D. Millers , K. Smits , A. Sarakovskis , W. Lojkowski , A. Swiderska-Sroda , W. Strek ,
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
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