The cryostat 1 was worked out, helped to deform the crystals at 80 K with different degree of deformation and to register luminescence, absorption and thermally activated characteristics of crystals, also to record the ionic and thermally stimulated currents of the dipole defects of depolarization. The degree of crystals deformation is given by compressing screw pitch which is equal to 1mm at a complete revolution of the crystal holder. The construction of the cryostat allows to set experimentally the desired degree of crystals deformation. Deformation can be removed from the crystal and re-update at different temperatures.
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.
Using X-ray luminescence spectra, the enhancement of both σ-luminescence of self-trapped excitons and Ех luminescence (band maxima at 3.89 and 3.1 eV, respectively) has been revealed for the first time in RbI single crystals exposed to elastic uniaxial stress at 93 K. The intensity of these emissions increases linearly with the relative degree of applied uniaxial deformation of the crystal up to ɛ = 1%, while the luminescence undergoes saturation at higher values of ɛ. The behavior of the I = f (ɛ) dependence for σ and Ех emissions suggests that Ех luminescence is intrinsic, and is connected with the radiative relaxation of self-trapped excitons in the field of local deformation of a RbI regular lattice.
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