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
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
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
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
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
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)