zirconia

Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition

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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
luminescence.
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

http://dx.doi.org/10.1016/j.optmat.2014.06.003

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

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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
applications

Journal of Applied Physics 115, 213520 (2014)

DOI:10.1063/1.4882262

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

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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
applications.

VC 2014 AIP Publishing LLC.

doi: 10.1063/1.4882262

http://dx.doi.org/10.1063/1.4882262

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Up-conversion luminescence dependence on structure in zirconia nanocrystals

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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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Nanocomposites for Novel Sensing Systems

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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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Zirconia nanocrystals as submicron level biological label

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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

doi:10.1088/1757-899X/38/1/012050

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Europium doped zirconia luminescence

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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

doi:10.1016/j.optmat.2010.03.002

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Luminescence of oxygen related defects in zirconia nanocrystals

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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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