«ANNUAL REPORT Riga 2012 Annual Report 2011, Institute of Solid State Physics, University of Latvia. Editor: A.Krumins. Composed matter: A.Muratova. ...»
Synthetic silica glass with an optical absorption spectrum dominated by oxygen dangling bonds (nonbridging oxygen hole centers, or NBOHCs) and having negligible (1%) contribution from the usually co-present Si dangling bonds (E'γ-centers), was prepared by room temperature ultraviolet photobleaching of high SiOH content (“wet”) silica, irradiated by F2 laser (7.9 eV) at T=80 K. This allowed us to obtain the up-to-now controversial optical absorption spectrum of NBOHC in the ultraviolet and vacuum-ultraviolet (UV-VUV) region of the spectrum and to show that it is semicontinuous from 4 to 7.8 eV and cannot be represented by a pair of distinct Gaussian bands. Since NBOHC is one of the main UV-VUV range optical absorbers in silica, its spectral shape provides a tool to disentangle contributions of different color centers to optical losses in this spectral region.
The target is description of the properties of localized states in silica glass. It has been observed that laser light interaction with localized states of silica glass leads to creation of luminescence centers. Created luminescence centers, excited with laser light, provide intra-center luminescence of oxygen deficient centers (ODC). Beside these processes laser light can give rise to charge separation. Recombination of created electrons and holes leads to recombination luminescence, a cause of the prolongation of some fast in intra-center process luminescence. Evidence has been given that center of recombination at ODC sites involves an electron trap at the defect, whereas the hole is created as a self-trapped hole center. Recombination results in the localized state recovering its initial state with disappearance of the transiently created luminescence center.
Such recombination is of luminescence of long duration in contrast with intra-center processes which are limited in time and we observe a shortened duration of such luminescence. Studies of temperature dependences of recombination luminescence intensity and decay show that intensive changes in these parameters take place in the known range of temperatures of self-trapped hole liberation. Decrease of measured recombination luminescence duration is followed with less rapid decrease of recombination luminescence intensity. In some times the luminescence intensity even grows with heating, when decay kinetics is accelerated. As a rule, luminescence decay curves are non-exponential well described with stretched exponential function, showing first order fractal-kinetics. It is argued that discovered localized states of silica glass are connected with structure other than tetrahedrons. In dense silicon dioxide crystal with rutile structure (stishovite) luminescence similar to ODC luminescence of silica glass has been found.
Main luminescence of α-quartz crystal doped with germanium is luminescence of a selftrapped exciton near germanium. The luminescence characteristic for silica glass doped with germanium – so call GeODC – never was observed in as grown Ge-doped α-quartz crystal.
Now we had performed experiment if GeODC like luminescence could appear after γirradiation of Ge-doped α-quartz crystal. The answer is positive: a new luminescence with two bands – a blue one with time constant about 100 μs under pulsed light of ArF laser (193 nm) and an UV one with fast decay ~1.5 ns under the same excitation appears and it is resembling the GeODC luminescence of silica glass. Beside under excitation of F2 excimer laser (157 nm) the old STE luminescence remains in the sample irradiated. However, evident differences are obtained to the induced center with respect to known the twofold coordinated Ge center. The excitation with KrF laser does not provide decay time constant about 100 μs but provide blue luminescence with a faster decay about 4 μs. The pulses of ArF laser also excite this component of decay for the blue band. That we connect with multiformity of γ-ray created centers in amorphous areas of the Ge-doped crystal.
LUMINESCENCE IN GeO2-SiO2 FILMS FABRICATED BY SPCVD
A line of Ge-doped silica films 10-20μ in thickness were synthesized by the surface-plasma chemical vapor deposition (SPCVD) on silica substrates. The content of Ge in different films was varied as n·GeO2-(1-n) ·SiO2 with n changing from 0.02 to 1. No luminescence was observed in as received films under the excitation by 5 eV UV photons. It was the reason to conclude that the twofold coordinated germanium center is not formed immediately during the film preparation by SPCVD. However, subsequent heat treatment of the films by a CO2 laser beam leads to the appearance of luminescence as well as to a huge grows of the absorption band at 5 eV, which indicates to the presence of twofold coordinated germanium centers. This observation correlates with the case of Ge implanted silicon dioxide thin films, in which luminescence of the twofold coordinated germanium was found to increase several hundreds times after the heat treatment. In pure (without silicon) GeO2 SPCVD films the twofold coordinated germanium centers were not revealed even after heat treatment.
However, under an ArF excimer laser (193 nm wavelength) excitation some luminescence is observed in the non-treated films with intensity increase at cooling down to 80 – 60 K. The decay kinetics of this luminescence significantly differs from that of the twofold coordinated germanium center, although its spectral content is similar.
1. L.Grigorjeva, D.Millers, K.Smits, A.Sarakovskis, W.Lojkowski, A.Swiderska-Sroda, W.Strek, P.Gluchowski. The time-resolved luminescence characteristics of Ce and Ce/Pr doped YAG ceramics obtained by high perssure technique. Optical Mater., 2011 (article in Press).doi.:10.1016/j.optmat.2011.05.023.
2. K.Smits, L.Grigorjeva, D.Millers, A.Sarakovskis, J.Grabis, W.Lojkowski. Intrinsic defects related luminescence in ZrO2. J.of Lumin., 2011, 131 (10) pp.2058-2062.
3. R.Zabels, F.Muktepavela, L.Grigorjeva. Deformation behavior of nanostructured ZnO films on glass. Thin Solid Films., 2011 (Article in Press), doi.:10.1016/j.tsf.2011.10.150.
4. A.N.Trukhin, K.Smits, A.Sarakovskis, G.Chikvaidze, T.I.Dyuzheva, L.M.Lityagina.Luminescence of dense, octahedral structured crystalline silicon dioxide (stishovite). J.of Lumin., 2011, 131 (11) pp.2273-2278.
5. A.N.Trukhin, K.Smits, G.Chikvaidze, T.I.Dyuzheva, L.M.Lityagina. Luminescence of silicon dioxide – silica glass, α-quartz abd stishovite. Cent. Eur. J. of Physics, 2011, 9 (4) pp.1106-1113.
6. A.N. Trukhin, Luminescence of localized states in silicon dioxide glass. A short review, Journal of Non-Crystalline Solids, 2011, 357 pp. 1931–1940.
7. A.N.Trukhin,A.Boukenter,Y.Ouerdane,S.Girard, γ-ray induced GeODC(II) centers in germanium doped α–quartz crystal, Journal of Non-Crystalline Solids, 2011, 357 pp.
8. L.Grigorjeva, D.Millers, J.Grabis, Dz.Jankovica. Photoluminescence and photo-catalytic activity of zinc tungstate powders. Cent. Eur. J. of Physics, 2011 9 (2) pp.510-514.
9. K. Kajihara, T.Miura, H.Kamioka, M.Hirano. L.Skuja, H.Hosono, Exchange between interstitial oxygen molecules and network oxygen atoms in amorphous SiO2 studied by O isotope labeling and infrared photoluminescence spectroscopy. Phys.Rev. B83, 064202 (2011).
10. L. Skuja, K.Kajihara, M.Hirano, H.Hosono, Crucial dependence of excimer laser toughness of “wet” silica on excess oxygen J. Non-Crystalline Solids v.357 p.1875–1878 (2011) (doi:10.1016/j.jnoncrysol.2010.12.047).
11. K. Kajihara, M.Hirano, L.Skuja, H.Hosono Oxygen-excess amorphous SiO2 with 18Olabeled interstitial oxygen molecules J. Non-Crystalline Solids v.357, No 8-9, p.1842K. Kajihara, M.Hirano, L.Skuja, H.Hosono Frenkel defect process in amorphous silica Proc. of SPIE Vol. 8077 80770R-1 (2011).
13. L. Skuja, K.Kajihara, M.Hirano, A.Silins, H.Hosono Effects of temperature on electron paramagnetic resonance of dangling oxygen bonds in amorphous silicon dioxide, IOP Conf. Series: Materials Science and Engineering 23 (2011) 012016
14. L. Skuja, K. Kajihara, M. Hirano, H. Hosono, Visible to vacuum-UV range optical absorption of oxygen dangling bonds in amorphous SiO2, Phys.Rev.B 84, 205206 (2011) [9 pages].
Lectures in Conferences
International Baltic Sea Region Conference "Functional materials and nanotechnologies 2011 (FM&NT)", April 05-08, Riga, Latvia.
1. Dz.Jankovica, J.Grabis,L.Grigorjeva, D.Millers, K.Smits, L.Bukonte. Synthesis and characterization of Cerium and Europium Doped Nanocrystals. Book of Abstracts. P.97.
2. A.Swiderska-Sroda, K.Galazka, W.Lojkowski, T.Chudoba, A.Opalinska, K.Smits, L.Grigorjeva, D.Millers, C.Leonelli. Optical Oxigen Nano-sensor. Book of abstracts, p.24
3. K.Galazka, A.Swiderska-Sroda,, W.Lojkowski, T.Chudoba, A.Opalinska, K.Smits, L.Grigorjeva, D.Millers, C.Leonelli. Heat Treatment Effect on the ZrO2 +Eu Nanopowder Luminescence. Book of abstracts, p.93.
4. D.Millers, K.Smits, L.Grigorjeva. Short Lived and Stable Defects in Yttrium Stabilized Zirconia Simgle crystal. Book of abstracts, p.47.
5. R.Zabels, F.Muktepāvela, L.Grigorjeva, K.Kundziņš. Effec of Nanopowder Morphology on the Properties of ZnO Sintered Ceramics. Book of abstracts, p.196.
6.K.Smits, D.Millers, Dz.Jankoviča, L.Grigorjeva. The Luminescence of Eu Doped ZrO2 Nanocrystals. Book of abstracts, p.94.
7. K.Smits, A.Sarakovskis, D.Millers, Dz.Jankoviča, L.Grigorjeva. Up-conversion Luminescence in ZrO2 Nanocrystals. Book of abstracts, p.95.
8. L.Skuja, K.Kajihara, M.Hirano, A.Silin, H.Hosono "Effects of temperature on electron paramagnetic resonance of dangling oxygen bonds in amorphous silicon dioxide", paper ORAbstracts, p. 60.
9. A.N.Trukhin, A. Boukenter, Y. Ouerdane, S.Girard, „γ-ray-induced GeODC(II) centers in germanium doped α-quartz crystal”, Book of abstracts, p. 92.
10. Anatoly Trukhin, Konstantin Golant, Janis Teteris, „Luminescence in GeO2-SiO2 films fabricated by SPCVD”, Book of abstracts, p. 91.
LU CFI 27th Scientific Conference, 2010, 17-19 Febr., Riga, Latvia
1. L.Bukonte, L.Grigorjeva, V.Tupureina, D.Millers, M.Knite. YAG un ZnO nanopulveru/plimēru kompozītu optiskās īpašības. Abstracts, p.38 (oral).
2. J.Rikveilis, L.Grigorjeva, D.Millers, K.Smits. Oksīdu nanopulveru fotokatalīzes efektivitātes pētījumi. (poster).
3. V.Liepiņa, Dz.Jankoviča, K.Smits, D.Millers. Luminiscento īpašību atkarība no aktivēta stroncija alumināta sintēzes un pēcapstrādes (poster).
3. A. Trukhin, Localized states in silica. A short review., Abstracts, p.80 (oral).
11th International Conference on Inorganic Scintillators and Their Aplications.September., 11-16, 2011, Giessen, Germany.
1. D.Millers, K.Smits, L.Grigorjeva. Luminescence of cerium doped zirconi nanocrystals.
Program and Abstract Book, P1.21.
2. L.Grigorjeva, D.Jankoviča, K.Smits, D.Millers, S.Zazubovich. Luminescence of Ce, Pr and Ce/Pr doped nanopowders. Program and Abstract Book, P2.13.
18th International Workshop on Room Temperature Semiconductor X-ray and Gamma-Ray Detectors, 23-29 October, 2011, Valencia, Spain
1. V.Ivanov, P.Dorogov, A. Loutchanski, L.Alekseeva, L.Grigorjeva, D.Millers. Impoving the performance of CdZnTe Detectors Using Infrared Stimulation. Abstracts, RTSD S-2462.
2. L.Aleksejeva, P. Dorogov, V.Ivanov, A. Loutchanski, L.Grigorjeva, D. Millers.
Investigation of the Influence of Light Illumination on the Characteristics of CdZnTe Detectors. Abstracts, RTSD S-2463.
2th International Conference on Bio-Sensing Technology. 10-12 October, 2011, Amsterdam, the Netherland.
K.Smits, J.Liepins, M.Grube, M.Gavare, D.Jankovica, A.Sarakovskis. ZrO2 nanocrystals as a temperature probe in baker’s yeast Saccharomyces cerevisiae cells. Abstracts, P125.
The 19th University Conference on Glass Science August 3-5, 2011, Rensselaer Polytechnic Institute, Troy, New York 12180, USA K.Kajihara, L.Skuja, H.Hosono 18O labeled interstitial oxygen molecules as a probe to study reactions involving oxygen-related species in amorphous SiO2.
16th Internat. Conf. "Radiation Effects in Insulators", REI-16, Beijing, China, August 15-19, 2011 L.Skuja, K.Kajihara, M.Hirano, H.Hosono Point defects in glassy/amorphous SiO2 and related materials, paper I-3(invited), Abstract book, p.36.
Doctoral thesis Mihails Šorohovs. TlBr crystal optical, electrical and surface properties investigation; X-ray and γ-ray detectors development. Rīga, 2011.
Master thesis Laura Bukonte. Polimēru/oksīdu nanopulveru kompozītu luminiscentās īpašības, RTU, 2011
Research Areas The Department of Ferroelectric Physics is engaged in basic and applied research and education activities focused on studies of functional ferroelectric oxide materials including theoretical modelling, synthesis, processing, and characterization.
Material preparation methods.
Synthesis and processing of bulk ceramics samples is based on solid state reactions of oxides and carbonates exploiting synthesis at atmospheric pressure as well as two-stage hot pressing technologies.
Include X-ray diffraction, atomic force microscopy, piezo-response force microscopy, electron scanning microscopy with EDX option, EPR and Raman spectroscopies, dielectric impedance and hysteresis measurement tools, piezoelectric properties and field induced deformation, electrocaloric effect, ellipsometry and reflectometry techniques, adaptive optics.
• Phase transitions and ordering effects in “ordinary” ferroelectrics and ferroelectric relaxors along with new compositions, including multi-component systems containg admixtures and materials based on niobates and tantalates of alkaline and earthalkaline elements without lead;
• Theoretical research is focussed on quantum theories and computer simulations addressing the intrinsic localized excitations in nonlinear lattices: heuristic explanation of the nature of polar nano-regions in advanced complex oxides;
• Transition-element doping effects in ABO3 perovskites;