PhD thesis has been defended

The defense of the PhD thesis titled "Formation of luminescent centers in CeO2-x nanocrystals" by Maksimchuk P.O., the junior research scientist of Institute for Scintillation Materials of NAS of Ukraine, has been held on April 22, 2015.

Thesis for a scientific degree of candidate of science in physics and mathematics by specialty 01.04.10 – Physics of Semiconductors and Dielectrics. – Institute for Single Crystals, Kharkiv, 2015.

The thesis is devoted to the study of the effect of oxygen stoichiometry and size of nanocrystals on the luminescence properties of CeO2-x nanocrystals. In the thesis it was shown that luminescence of CeO2-х is determined by two optical centres of different nature: the first one is Ce4+-O2- complex and the second one - Ce3+ ions. Investigation of splitting of Ce3+ 4f→5d luminescence excitation band has shown that reduction of Ce4+ occurred mainly by the mechanism of oxygen vacancy formation on the nearest-neighbour position to the cerium ion. The ratio of Се4+-О2- and Се3+-ions intensities of luminescence bands strongly depends on the oxygen non-stoichiometry. By means of two independent spectroscopic techniques (using intensity of 5d→4f luminescence of Ce3+ ions and 5D0→7F1/5D0→7F2 ratio of Eu3+ bands as indicators of the concentration of oxygen vacancies) the sufficient increase of vacancy concentration with decrease of the size of CeO2-x nanocrystals was determined.

Keywords: luminescence, nanocrystal, rare-earth ion, cerium oxide, oxygen vacancy, charge transfer complex.

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