Vasyukov S. Radiation induced processes in the europium doped dielectric crystals NaI and CsI

This dissertation work is devoted to elucidation of mechanisms for the relaxation of energy excitations in NaI and CsI crystals as well undoped and co-doped Tl and Eu ions. This study is devoted to the analysis of emission efficiency loss in CsI and NaI based scintillators. Europium concentration was varied from 10-4 to 10-1mass%. The luminescence spectra were measured under photo-, X-ray and synchrotron excitation in the range 10 - 300 K. It was shown that in CsI:Eu and NaI:Eu crystals at low temperatures (<100 K), when the holes become self-trapped and STE form, the energy transfer from STE to Eu-related centers becomes the dominant due to reabsorption. At room temperature for NaI:Eu, similarly with NaI:Tl, the energy transfer process has a recombinational nature, namely it is related with a consecutive capture of excitations by the activator centers. In case of CsI:Eu the energy transfer from lattice to activator is very weak at room temperature. The mechanisms of energy transfer from Tl to Eu centers in the NaI:Tl, Eu crystals under ionizing radiation were studied. It is shown that the light output of crystals NaI: Tl, Eu higher by 10-15% compared to the same parameter for NaI:Tl. The co-doping by Eu and Tl ions allows to modify the spectral-kinetic characteristics and improve the effectiveness of scintillation material.