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48. Photoluminescence and Optical Absorption of Pure Nanocrystalline TiO2 Anatase and Rutile at Room Temperature.

Author

Kernazhitsky, L., Shymanovska, V., Gavrilko, T., Naumov, V., Fedorenko, L., and Kshnyakin, V.

Subjects
TITANIUM dioxide, NANOCRYSTALS, EXCITON theory, QUANTUM theory, QUASIPARTICLES
Abstract

The optical absorption and photoluminescence of nanocrystalline TiO2 samples of anatase and rutile were investigated at room temperature. Nanocrystalline TiO2 samples were synthesized in the form of pure anatase or rutile and studied by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL). PL was studied at room temperature when excited by intense UV (3.68 eV) by a nitrogen laser. For the first time for nanocrystalline TiO2 a features in the high-resolution PL spectra, including the exciton band and interband transitions were registered. It is concluded that the processes of absorption and emission of light near the edge of the forbidden zone occur with the participation of the same electronic transitions. PL bands, including the peaks at 2.71-2.81 eV in the anatase and rutile arise due to exciton recombination in the TiO2 lattice oxygen vacancies. The exciton peak at 2.91 eV is attributed to the recombination of self-trapped excitons in anatase or to the free exciton in rutile, respectively. PL bands within 3.0-3.3 eV attributed to indirect and direct allowed transitions due to electron-hole recombination. PL bands at 3.03 eV and 3.26 eV, attributed to the emission of free excitons near the fundamental absorption edge of rutile and anatase, respectively. The influence of TiO2 crystal structure and calcination temperature of the samples on the PL spectra and optical absorbtion is discussed. [ABSTRACT FROM AUTHOR]

Published
2013

49. 127I NQR and spectroscopic investigation of impurity-doped and mixed lithium iodate Li1-xHxIO3 crystals

Author

Barabash, A., Gavrilko, T., Eshimov, K., Baran, J., and Ratajczak, H.

Subjects
*CRYSTAL lattices, *LATTICE theory, *RAMAN spectroscopy, *SOLID state physics
Abstract

The 127I NQR, IR absorption and Raman spectra of impurity-doped and mixed lithium iodate Li1-xHxIO3 crystals grown from water solutions with different LiIO3/HIO3 ratios were investigated depending on the content of the impurity hydrogen x. The NQR results suggested that, at small concentration of doping iodic acid x<0.22, the lattice dynamics of the crystal grown from water solution changes significantly though the crystal retains hexagonal symmetry. Spectroscopic studies are compatible with average hexagonal symmetry of the grown doped crystals. From the results of Raman studies at room temperature and 100 K, the concentration range of hydrogen dopant 0.22 was found where disordered solid solution crystals Li1-xHxIO3 are formed. [Copyright &y& Elsevier]

Published
2004
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50. Possible manifestation of proton disorder in δ-KIO3·HIO3 crystal in its IR spectra

Author

Gavrilko, T., Puchkovska, G., Sekirin, I., Engelen, B., Panthöfer, M., Baran, J., and Ratajzcak, H.

Abstract

For getting more information about the behavior of hydrogen atoms in partially occupied sites in δ-KIO3·HIO3, we have measured temperature-dependent infrared spectra of this crystal at 14–300 K in the spectral range of OH stretching and bending vibrations. It was found that ν(OH) band (centered at ∼2800 cm−1) has complicated profile which, at temperatures below 220 K, includes weak low-frequency satellites at its low-frequency slope. At 14 K, we have main peak ν(OH) at 2766, satellites at 2606, 2485, and 2387 cm−1, and strong 2δ(OH) overtone peak at 2274 cm−1 enhanced due to Fermi resonance. At the same time, the low-frequency slope of δ(OH) band (centered at 1189 cm−1) shows equidistant satellites separated with period of approximately 25 cm−1. The observed features suggest anharmonic coupling between OH high-frequency vibrations and various low-frequency motions of the crystal lattice. [Copyright &y& Elsevier]

Published
2004
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