The specifics of radiative annihilation of self-trapped excitons in a KI–Tl crystal under low-temperature deformation

Abstract

The effect of low-temperature uniaxial deformation on the self-trapping-limited mean free path of excitons in a KI–Tl crystal was revealed from x-ray luminescence spectra. The analysis of the dependence of the intensity ratio of the Tl-center emission (2.85 eV) and the luminescence of self-trapped excitons (π-component; 3.3 eV) on the extent of low-temperature deformation showed that in the KI–Tl crystal (3 × 10−3 mol. %) the self-trapping-limited mean free path of excitons is comparable with the distance between Tl atoms (20–27)a under a deformation ε = 2%. As the compression increases to ε ≥ 2%–5%, the mean free path drops to (27-5.35)a. The results of modeling based on the continuum approximation showed that with increasing temperature and the degree of low-temperature deformation the height of the potential barrier for the exciton self-trapping drops, which is consistent with the reduction of the mean free path of excitons in the KI–Tl crystal.

The features of deformation-stimulated RbI luminescence

“…According to the proposed scheme, the increase in the intensity of STEs luminescence in the AHCs occurs due to a reduction in the free path of unrelaxed excitons before self-trapping, which will lead to an increase in the probability of self-trapping in regular lattice nodes [15].…”

“…In the experimental plan, elastic deformation is successfully used not only as a method of influencing the relaxation processes of STEs, but also for recognizing the nature of luminescence in AHCs [15]. For the first time, low-temperature uniaxial elastic deformation was used as an external perturbing factor that reduces the lattice symmetry to solve the problem of the intrinsic or impurity nature of E x -luminescence in KI and RbI crystals [16].…”

“…For the first time, low-temperature uniaxial elastic deformation was used as an external perturbing factor that reduces the lattice symmetry to solve the problem of the intrinsic or impurity nature of E x -luminescence in KI and RbI crystals [16]. The intensity of intrinsic luminescence of exciton nature correlates with an increase in the degree of elastic deformation, and the intensity of luminescence of impurity nature, on the contrary, will decrease until it disappears, since the transfer of exciton energy to impurities will worsen due to the inclusion of the mechanism of their self-trapping in regular lattice sites [15].…”

Radiation defects in NaCl matrix with reduced lattice symmetry caused by light cation doping and elastic uniaxial deformation

“…This conclusion was firstly based on the experimentally detected redistribution of the intensity of impurity luminescence (thallium-related, peaked at 2.85 eV) in favour of the π-STE emission (3.3 eV) in a KI:Tl crystal exposed to elastic deformation [46]. This enhancement of the intrinsic luminescence of KI:Tl with an elastic deformation degree at 90 K was interpreted as a consequence of the reduction in the free path of the mobile anion exciton before their self-trapping.…”