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«ANNUAL REPORT Riga 2012 Annual Report 2011, Institute of Solid State Physics, University of Latvia. Editor: A.Krumins. Composed matter: A.Muratova. ...»

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1. National Institute for Materials Physics (INCDFM), Bucharest, Romania (Dr. M. Secu)

2. National Institute for Research and Development for Optoelectronics INOE 2000, Bucharest, Romania (Dr. I. C. Vasiliu)

–  –  –

We investigated the EPR superhyperfine structure of the Mn2+ ion in the disordered BaF2 crystalline media which tends to crystallize in the oxyfluoride glass-ceramics material.

Obtained EPR spectra reveal explicit shf structure due to Mn2+ ion building into the BaF2 lattice showing its usefulness as a probe in orientationally disordered and amorphous structures. Two types with explicit shf structure of Mn2+ ion characteristic EPR spectra were obtained in BaF2 powder samples characteristic with broad (type 1) and narrow (type 2) hyperfine structure lines. Spectra of the ZnF2-BaF2 oxyfluoride glass-ceramics samples revealed explicit fine structure lines.

–  –  –

In this work we tried to achieve multicolor up-conversion luminescence in low phonon energy material NaLaF4 doped with different Er3+; Tm3+ and Yb3+ concentrations. Up-conversion luminescence was measured and main luminescence bands from Er3+ and Tm3+ in red, green and blue spectral regions were observed. The relative intensities of the luminescence bands could be changed by changing the doping levels of rare-earth ions. Changes in the upconversion luminescence color could be achieved by applying different infrared pump power density. The color coordinates of the multicolor up-conversion luminescence depending on doping level as well as on the pump power density were presented in CIE (x, y) chromaticity diagram (1931).

–  –  –

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.

–  –  –

I Tale, L Dimitrocenko, P Kulis, G Marcins, A Sarakovskis and A Voitkans Picosecond time resolved photoluminescence (PL) spectroscopy of excitonic processes in MOCVD grown InxG1-xN mixed films with the In concentration in range from x=0.1 to 0.18 under the band-to-band excitation are considered. It is stated that by an In content in alloy up to 12% the band-band photo excitation at 8 K results in creating of localized excitons and biexcitons represented by close overlapping Gaussian shape luminescence bands having FWHM 27 and 8.7 meV, respectively. PL decay kinetics of both bands involves two exponential decay stages. Excitons and biexcitons in unperturbed lattice positions causes fast decay with τ ~ 10 ps, whereas their transfer to the metastable state due to relaxation of In – Ga local configuration causes slow decay τ ~ 90 ps At increased In content up to 19% both the localized excitons and biexcitons are represented by Gaussian type luminescence bands being non-uniform broadened to the high energy side. The continuous distribution of excitons and biexcitons in transition energies is stated by analysis of the red-shift of luminescence bands during the spectra decay. An additional new narrow low energy PL band arises at low energy side expected to be caused by excitons at InN clusters.

–  –  –

Appropriate methods for investigating the effects of plasma exposure are required in order to improve and develop new plasma-facing components. Particle fluxes from plasma result in complex plasma-wall interactions causing phenomena such as erosion and migration of materials, retention, co-deposition and diffusion. Several methods of analyzing the surface and impurity content in the near-surface layers are currently employed. An alternative method of establishing the impurity content in solid materials is laser-induced breakdown spectroscopy. This powerful tool for spectro-chemical analysis provides both impurity content analysis and layer-by-layer depth profiling. We present spectral information and discuss questions regarding the depth profiles of the impurities.

–  –  –

Nanocrystalline silicon films were deposited by a picosecond laser ablation on different substrates in vacuum at room temperature. A nanocrystalline structure of the films was evidenced by atomic force microscopy (AFM), optical and Raman spectroscopy. A blue shift of the absorption edge was observed in optical absorption spectra, and a decrease of the optical phonon energy at the Brillouin zone centre was detected by Raman scattering. Early stages of nanocrystalline film formation on mica and HOPG substrates were studied by AFM.

Mechanism of nanocrystal growth on substrate is discussed.

Scientific publications

1. G. Marcins, J. Butikova, I. Tale, B. Polyakov, R. Kalendarjov, A. Muhin.

Crystallization processes of amorphous Si by thermal annealing and pulsed laser processing, IOP Conf. Ser.: Materials Science and Engineering 23, p.012035, 2011.





2. B. Polyakov, L. Dorogin, S. Vlassov, I. Kink, A. Lohmus, A. Romanov, R. Lohmus.

Real-time measurements of sliding friction and elastic properties of ZnO nanowires inside a scanning electron microscope. Solid State Communications, 151, 1244–1247, 2011.

3. S. Vlassov, B. Polyakov, L. Dorogin, A. Lõhmus, A. Romanov, I. Kink, E. Gnecco, R.

Lõhmus. Real-time manipulation of gold nanoparticles inside a scanning electron Microscope. Solid State Communications, 151, 688, 2011.

4. B. Polyakov, L. Dorogin, A. Lohmus, A. Romanov, R. Lohmus. In situ measurement of the kinetic friction of ZnO nanowires inside a scanning electron microscope. Applied Surface Science. 258, 3227-3231, 2012.

5. L. Dimitrocenko, P. Kulis, A. Sarakovskis, I. Tale, A. Voitkans, Dynamics of exciton

creation and decay processes in composition- disordered InGaN thin films, IOP Conf. Ser.:

Mater. Sci. Eng. 23 (2011) 012001.

6. L. Dimitrocenko, K. Kundzins, A. Mishev, I. Tale, A. Voitkans, P. Kulis, Growth temperauture influence on the GaN nanowires grown by MOVPE technigue, IOP Conf.

Ser.: Mater. Sci. Eng. 23 (2011) 012026.

7. A. Voitkans, L. Dimitrocenko, S. Bartlin, I. Barke, K.-H. Meives-Broer, P. Kulis, I. Tale, Ex situ investigations of MOCVD-grown gallium nitride nanowires using reflection high energy electron diffraction, IOP Conf. Ser.: Mater. Sci. Eng. 23 (2011) 012038.

8. A. Sarakovskis, M Voss, G Doke, J Grube and M Springis, Novel synthesis of upconversion phosphor based on rare-earth doped NaLaF4, - IOP Conf. Series: Materials Science and Engineering, 2011, 23, 012003.

9. J Grube, G Doke, M Voss, A Sarakovskis and M Springis, Multicolor Up-Conversion Luminescence in Rare-Earth Doped NaLaF4,- IOP Conf. Series: Materials Science and Engineering, 2011, 23, 012004.

10. K. Smits, L. Grigorjeva, D. Millers, A. Sarakovskis, J. Grabis, W. Lojkowski, Intrinsic defect related luminescence in ZrO2, - Journal of Luminescence, 2011, 131, 2058-2062.

11. A. Fedotovs, Dz. Berzins, O. Kiselova, A. Sarakovskis and U. Rogulis, Analysis of

Mn2+ EPR spectral shapes for studies of the oxyfluoride glass ceramics IOP Conf. Ser.:

Mater. Sci. Eng., 2011, vol. 23, 012018, doi:10.1088/1757-899X/23/1/012018.

12. L. Dorogin, B. Polyakov, A. Petruhins, S. Vlassov, R. Lohmus, I. Kink, A. Romanov.

Modeling of kinetic and static friction between an elastically bent nanowire and a flat surface. Journal of Material Research. 2012. In press.

Lectures on Conferences

27th Scientific Conference of the Institute of Solid State Physics, University of Latvia, Riga, 2011, February 14-16

1. J. Butikova, I. Tale, Estimation of the concentration of atoms using parameters of plasma in local thermodynamic equilibrium, - Abstracts of the 27th Scientific Conference ISSP LU, 2011, p. 7.

2. I. Tale, A. Voitkans, J. Butikova, Spectroscopy of Ga vapour concentration and dynamics in Tokamak plasma. Project WP10/PWI-05-0401/ULV/PS, - Ibid., p. 8.

3. J. Smits, A. Sarakovskis, G. Kucinskis, G. Bajars, J. Kleperis, Electrochemical properties, structure and morphologyof LiFePO4 thin films annealed by different methods, - Ibid., p.

30.

4. J. Grube, G. Doke, M. Voss, A. Sarakovskis, M. Springis, Up-conversion luminescence in NaLaF4 with different Er3+ concentrations, - Ibid., p. 52.

5. I. Brice, U. Rogulis, E. Elsts, A. Sarakovskis, G. Doke, Activated oxyflourides for solidstate lighting, - Ibid., p. 53.

6. G. Doke, M. Voss, J. Grube, A. Sarakovskis, M. Springis, Up-conversion luminescence of erbium and ytterbium doped NaLaF4 material, - Ibid., p. 81.

7. Dz. Berzins, A. Fedotovs, U. Rogulis, A. Sarakovskis, EPR hyperfine structure of radiation defect in oxyflouride glass ceramics, - Ibid., p. 82.

8. A. Fedotovs, Dz. Berzins, O. Kiselova, A. Sarakovskis, Paramagnetic impurities for oxyflouride glass ceramics structure studies, -. Ibid., p. 83.

9. J. Jansons. Pusvadītāju fizikas problēmu laboratorijas izveides priekšnosacījumi. – Ibid., p. 92-96.

10. I. Tāle, Jonu kristālu pētījumi Pusvadītāju fizikas problem laboratorijā, - Ibid., p. 111International conference “Functional materials and nanotechnologies” FM&NT, Riga, 2011, April 5 -8

1. L. Dimitrocenko, P. Kulis, A. Sarakovskis, I. Tale, A. Voitkans, Dynamics of exciton creation and decay processes in composition – disordered InGaN thin films, International conference „Functional materials and nanotechnologies” FM&NT 2011, Book of abstracts, ISSP LU, Riga, April 5 – 8, p 43.

2. A. Fedotovs, Dz. Berzins, O. Kiselova, A. Sarakovskis, U. Rogulis, Paramagnetic impurities for studies of the oxyflouride glass ceramics structure, -. Ibid., p. 61.

3. L. M. Dorogin, B. Polyakov, A. Petruhins, A. Lohmus, A. E. Romanov, I. Kink, R. Lohmus, Measurements of static and kinetic friction of ZnO nanowires on a flat surface, - Ibid., p. 74.

4. B. Polyakov, S. Vlassov, L. Dorogin, A. Romanov, A. Lohmus, R. Lohmus, Manipulation of gold nanoparticles inside scanning electron microscope, - Ibid., p. 84.

5. K. Smits, A. Sarakovskis,D. Millers, Dz. Jankovica, L. Grigorjeva, Up-conversion luminescence in ZrO2 nanocrystals, - Ibid., p. 95.

6. E. Elsts, U. Rogulis, J. Jansons, A. Sarakovskis, G. Doke, Cathodoluminescence of terbium and cerium activated oxyfluorides, - Ibid., p. 96.

7. G. Doke, M. Voss, J. Grube, A. Sarakovskis, M. Springis, Multicolour up-conversion luminescence in rare-earth doped NaLaF4, - Ibid., p. 98.

8. A. Sarakovskis, M. Voss, G. Doke, J. Grube, M Springis, Novel synthesis of upconversion phosphor based on rare-earth doped NaLaF4, - Ibid., p. 99.

9. P. Kulis, A. Petruhins, J. Butikova, B. Polyakov, I. Muzikante, I. Tale, Sulphide nanocrystals for solar cell applications, -. Ibid., p. 105.

10. J. Smits, A. Sarakovskis, G. Bajars, L. Grinberga, J. Kleperis, Examination of different approaches to LiFePO4 thin films laser annealing, - Ibid., p. 134.

11. Dz. Berzins, A. Fedotovs, U. Rogulis, Studies of radiation defect EPR hyperfine structure in oxyflouride glass ceramics, - Ibid., p. 138.

12. L. Dimitrocenko, K. Kundzins, A. Mishnev, I. Tale, A. Voitkans, P. Kulis, Growth temperature influence on the GaN nanowires grown by MOVPE technique, - Ibid., p.

192.

13. A. Voitkans, L. Dimitrocenko, S. Bartlin, P. Kulis, I. Tale, Ex situ investigations of MOCVD-grown gallium nitride nanowires using reflection high energy electron diffraction, - Ibid., p. 193.

14. I. Tale, J. Butikova, G. Marcins, A. Muhins, B. Polyakov, A. Voitkans, Crystallization processes of amorphous Si by pulsed laser processing, -. Ibid., p. 231.

16th International conference on Luminescence & Optical specctroscopy of condensed matter ICL'11, Ann Arbor, USA, 2011 E. Elsts, U. Rogulis, J. Jansons, A. Sarakovskis, Cathodoluminescence of terbium activated oxyfluorides,

Abstract

of the 16th International conference on Luminescence & Optical specctroscopy of condensed matter ICL'11, Ann Arbor, USA, 2011, TuP130.

11th International Conference on Inorganic Scintillators and their Applications SCINT'2011, Giessen, Germany

1. U. Rogulis, E. Elsts, J. Jansons, A. Sarakovskis, G. Doke, A. Stunda, K. Kundzins, Rare earth activated oxyfluoride glasses and glass-ceramics for scintillation applications, Abstract of the 11th International Conference on Inorganic Scintillators and their Applications SCINT'2011, Giessen, Germany, P 1.17.

2. Dz. Berzins, A. Fedotovs, U. Rogulis, Radiation defect in oxyfluoride glass ceramics:

EPR hyperfine structure, Abstract of the11th International Conference on Inorganic Scintillators and their Applications SCINT'2011, Giessen, Germany, P 1.18.

54th Scientific Conference for Young Students of Physics and Natural Sciences, Open Readings 2011, Vilnius, LITHUANIA I. Brice, U. Rogulis, E. Elsts, A. Šarakovskis, J. Grūbe, G. Doķe, Activated oxyfluorides for solid-state lighting, 54th Scientific Conference for Young Students of Physics and Natural Sciences, Open Readings 2011, Vilnius, LITHUANIA, 2011, PP-16, p. 96.

Popular Science Articles (in Latvian)

1. J. Jansons. LU fizikas docentam Egonam Zablovskim – 85. – „Zvaigžņotā Debess”,

2011. gada pavasaris (211), 34. – 39. lpp.

2. J. Jansons. Fiziķu centieni 1950.–1960. gados atgriezt fundamentālo zinātni Universitātē. – „Zvaigžņotā Debess”, 2011./12. gada ziema (214), 27. – 32. lpp.



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