Voloshyna L. Obtaining of luminescent composite materials based on nanoporous SiO2 matrices

The thesis is devoted to the development of the method for producing luminescent composite materials ZnSe nanocrystals/SiO2-matrix, organic phosphors o-POPOP/SiO2-matrix and PPO/SiO2-matrix and to the study of their luminescent and scintillation characteristics. The method of obtaining high-porous SiO2-matrix with stochastic type structure and pore sizes 2-5 nm, specific surface area of 400 - 900 m2/g and pore volume of 0,2 - 0,5 cm3/g was proposed. The methods of introduction of ZnSe nanocrystals and organic phosphors 1,2-bis(5-phenyloxazolyl-2)benzene (o-POPOP) and 2,5-diphenyloxazole (PPO) into SiO2-matrices were developed for obtaining luminescent composite materials with optimum content of active components. It was shown that ZnSe nanocrystals /SiO2-matrix composite materials can be effectively obtained by the method of growing of ZnSe nanocrystals directly inside SiO2-matrix. The size of ZnSe nanocrystals obtained in the pores of SiO2-matrix was equal to 2,5 - 3 nanometers. On the basis of the obtained experimental data the mechanism of temperature quenching of ZnSe luminescence for ZnSe bulk crystal and ZnSe/SiO2-matrix composite material was proposed. While for ZnSe crystal luminescence temperature quenching occurs with participation of the bottom of the conduction band, lower values of activation energy and shorter decay times for ZnSe/SiO2-matrix composite material show that the quenching occurs via direct phonon-assisted transfer of excitation energy to the defect sites of ZnSe lattice or SiO2-matrix. The method of obtaining POPOP/SiO2-matrix and PPO/SiO2- matrix composite materials by impregnation of SiO2-matrix by solutions of organic phosphors allows obtaining samples with the controlled content of organic phosphor from 2 mass.% to 20 mass.%. The composite materials possess high photoluminescence intensity, transparency in the visible range and decay times in the range of nanoseconds. Absolute light output for the o-POPOP/SiO2-matrix was equal to 5100 photons/MeV, for PPO/SiO2-matrix - 4400 photons/MeV. Light output is comparable to the light output of BC416 commercial plastic scintillator based on polyvinyl toluene (Saint Gobain Co.).