Trefilova L. Regularities of radiation formation of short-lived color centers and luminescence in scintillation crystals based on CsI

The thesis for the degree of Doctor of Physics and Mathematics, specialty 01.04.10 - Physics of Semiconductors and Dielectrics. - Institute of Single Crystals of NAS of Ukraine, Kharkiv, 2021. Systematically investigated are the processes of the formation of luminescent response to the action of short pulses of accelerated electrons and emission laser in the scintillation crystals CsI(A) (A ≡ Tl+, Na+, CO32–). The concept of the key role of the radiation-induced donor-acceptor dipoles [Tl0Vk], [Na0Vk] and [F,CO3], respectively, in the luminescence process, is proposed. The spectral and kinetic properties of luminescence excited by ionizing radiation are defined by a specific character of decay of the dipoles followed by the formation of two types of near-activator excitons which differ in the position of two-halide hole nucleus with respect to the neighboring cation- (Tl+ or Na+) or anion- (CO32–) substituting activator ion. The knowledge of the mechanism of population of radiative states for near-activator excitons in activated CsI crystals, is extended. In contrast to CsI:Na and CsI:CO3 crystals in which decay of donor-acceptor pairs occurs by electron tunneling from the ground level of the electron Na0 or F- (color) center, the population of radiative states of singlet Tl+-localized excitons is realized due to disintegration of donor-acceptor pairs in which thallium atom is present in excited metastable state, that defines a relatively longer duration of activator luminescence decay in CsI:Tl Keywords: cesium iodide crystals, activator luminescence, decay kinetics, two-halide exciton.