Viktoriia Levushkina will defend her doctoral thesis titled "Energy transfer processes in the solid solutions of complex oxides" on 15. June 2017 at 14.15 at W. Ostwaldi 1, room B103.
dr Dmitry Spassky, Moscow State University, Russia
prof Mikhail Brik , Institute of Physics, University of Tartu
dr Vladimir Makhov, Russian Academy of Sciences, Institute of Physics
The main goal of the thesis was set to demonstrate how the modification of the crystal composition affects the structural, electronic and optical properties of a series of borate, phosphate and vanadate crystals (LuxY1-xBO3, LuxY1-xPO4, LuxY1-xVO4, undoped and doped with Eu3+ or Ce3+). The chosen systems are widely used for lighting and scintillating applications. The isovalent cation substitution in the vanadates and the phosphates does not change the structure, but produces pronounced influence on the wide range of their physical properties. In particular, it was demonstrated that the gradual substitution of one cation (Lu) by another (Y) is accompanied by the linear variation of the structural parameters and, what is more important, by a non-linear variation of the emission intensity in such mixed compounds. The maximum emission intensity in the LuxY1-xVO4 system is realized when x=0.7. Such a phenomenon is explained by modification of the charge carriers free path that is caused by changes in the electronic structure. The optimal composition determined in the thesis can lead to improved performance of the phosphors and scintillators based on these materials. In addition, explanation of the observed results suggested in the thesis contributed to the basic understanding of processes of interaction of light with matter at the microscopic scale.