Alekseev V. Peculiarities of energy transfer in radiation-colored CsI:Tl crystals

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, 2018. The radiative damage of CsI:Tl crystals and the role of color centers induced by irradiation in the process of energy transfer to Tl+ luminescence centers are studied. It is found that deformation, thermal and optical processing of the crystal, as well as the presence of CO32- ions affect the processes of formation and relaxation of the activator color centers. The properties of the induced absorption are explained in terms of absorption of impurity vacancy dipoles Tl0va+ і Tl2+vс-, where the electronic Tl0 and hole Tl2+ centers are perturbed by a neighbor anionic va+ and cationic vс- vacancies, respectively. A volumetric conductivity current excited by near-ultraviolet arise due to the transfer of the electron from I- to the Tl+ ion in CsI:Tl crystal. The charge transfer initiates the formation of Tl0 center and the capture of the hole by the impurity vacancy dipole CO32-va+ with the formation of CO3- ion and the release of the anionic vacancy va+ to be captured by Tl0 center in the diffusion process. Tl0va+ and Tl2+vс- centers participate in scintillation process to get energy from Tl+ emission centers by resonance. Degradation of the light yield of а irradiated CsI:Tl crystal is due to the radiative energy transfer from Tl+ to Tl0va+ centers, whose emission is quenching at temperature above 210 K. Non-radiative energy transfer from Tl+ to Tl2+vc- centers results in long-wave spectral shifts and the duration increase of the scintillation pulse. Key words: cesium iodide, ion thallium, color center, charge transfer, luminescence, absorption, vacancy.