2014

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

Posted on by editor

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

DOI:10.1016/j.jlumin.2014.11.034

pdf-iconDownload PDF

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

Posted on by editor

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

pdf-iconDownload PDF

Luminescence of Phosphorus Containing Oxide Materials: Crystalline SiO2-P and 3P2O5·7SiO2; CaO·P2O5; SrO·P2O5 glasses

Posted on by editor

A. N.Trukhin, K. Smits, J. Jansons, D. Berzins, G. Chikvaidze,
D.L.Griscom

ABSTRACT. Luminescence of phosphate glasses such as CaO·P2O5 and SrO·P2O5 is compared with that of phosphorus doped
crystalline -quartz and phosphosilicate glass with content 3P2O5·7SiO2. Water & OH groups are found by IR spectra in these
materials. The spectrum of luminescence contains many bands in the range 1.5 – 5.5 eV. The luminescence bands in UV range at
4.5- 5 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also
a component in μs range was detected. PL band of μs component is shifted to low energy with respect to that of ~37 ns
component. This shift is about 0.6 eV. It is explained as singlet-triplet splitting of excited state. Below 14 K increase of
luminescence kinetics duration in μs range was observed and it was ascribed to zero magnetic field splitting of triplet excited
state of the center. Yellow-red luminescence was induced by irradiation in phosphorus doped crystalline -quartz,
phosphosilicate glasses. The yellowl uminescence contains two bands at 600 and 740 nm. Their decay is similar under 193 nm
laser and may be fitted with the first order fractal kinetics or stretched exponent. Thermally stimulated luminescence contains
only band at 600 nm. The 248 nm laser excites luminescence at 740 nm according to intra center process with decay time
constant about 4 ms at 9 K. Both type of luminescence UV and yellow were ascribed to different defects containing phosphorus.
P-doped α-quartz sample heated to 550 co become opalescent. Ir spectra related to water & OH groups are changed.
Photoluminescence intensity of all three bands, UV (250 nm), yellow (600 nm) and red (740 nm) strongly diminished and
disappeared after heating to 660 Co. Radiation induced red luminescence of non-bridging oxygen luminescence center (NBO)
appeared in crystal after heat treatment. We had observed a crystalline version of this center (l. Skuja et al, Nuclear Instruments
and Methods in Physics Research B 286,159–168 (2012)). Effect of heat treatment explained as sedimentation of phosphorus in
some state. Keeping of treated sample at 450-500 Co leads to partial revival of ability to create yellow luminescence center
under irradiation.

AIP Conf. Proc. 1624, 154-166 (2014);

doi: 10.1063/1.4900472

pdf-iconDownload PDF

Characteristic and sinterability of alumina-zirconia-yttria nanoparticles prepared by different chemical methods

Posted on by editor

GRABIS Janis, JANKOVICA Dzidra, STEINS Ints, SMITS Krisjanis,and SIPOLA Inta

Abstract. The characteristics and sinterability of the Al2O3-ZrO2(Y2O3) nanoparticles produced by
simple and effective microwave and molten salts methods and processed by using spark plasma
sintering were studied and compared. The crystalline powders with the specific surface area in the
range of 72–108 m2/g and crystallite size of 5–13 nm were obtained by calcination of samples
prepared by both methods at 800 oC. The content of t-ZrO2 phase depends on concentration of
Al2O3, Y2O3 and on calcination temperature but the impact of the preparation method is
insignificant. The phase transition of tetragonal ZrO2 to monoclinic for the samples without Y2O3
started at 1000 oC though it was incomplete in the case of high content of Al2O3. The bulk materials
with relative density of 86.1–98.7% were fabricated by the spark plasma sintering method at 1500–
1600 oC depending on the content of Al2O3 and Y2O3.

Advances in Science and Technology Vol. 87 (2014) pp 30-35

doi:10.4028/www.scientific.net/AST.87.30

pdf-iconDownload PDF

Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition

Posted on by editor

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

pdf-iconDownload PDF

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

Posted on by editor

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

pdf-iconDownload PDF

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

Posted on by editor

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

pdf-icondownload PDF

Luminescence of rutile structured crystalline silicon dioxide (stishovite)

Posted on by editor

A.N.Trukhin , K.Smits, G.Chikvaidze, T.I.Dyuzheva, L.M.Lityagina 

Luminescence spectrum of synthetic mono-crystalline stishovite comprises as low blue band at 400 nm
(3.1 eV) and a fast UV band at 260 nm (4.7 eV), as well as some bands in near-infrared range of spectra.The NIR luminescence of stishovite crystal, excited with lasers 532 nm, 248 nm and 193 nm as well as x-ray, possesses several sharp lines. Azerophonon line is situated at 787 nm (1.57 eV) and grows with cooling. An anti-Stokes line is located at 771 nm (1.68 eV). This line disappears with cooling. In a powder sample of stishovite created by shockwaves generated by the impact of a 50m-diameter meteorite in Arizona 50,000 years ago, the PL broad blue band is situated at 425 nm (2.9eV), the UV band at 260 nm (4.7eV), and the sharp lines, seen only under 193 nm laser, at 689 nm (1.789 eV), 694 nm (1.785 eV) and 706 nm (1.754 eV).
We ascribe the fast UV luminescence to singlet–singlet transitions and the slow blue band to triplet–
singlet transitions of the same intrinsic defect of stishovite in both types of samples. The blue band in
stishovite crystal exhibits delayed luminescence of recombination nature, whereas the blue band of Arizona’s powder sample does not exhibit such effect. This difference is explained by different surroundings of luminescence center in those samples. NIR luminescence of mono-crystalline stishovite is ascribed to carbon impurity penetrated in the sample from graphite heater. NIR luminescence of powder from Arizona has not yet found an explanation.

Solid State Communications 189(2014)10–14

DOI: 10.1016/j.ssc.2014.03.010

pdf-iconDownload PDF