The influence of deformation on off- and on-configuration of excitons in crystals CsI

It has been defined that in alkali halides crystals, the probability of self-trapped excitons (STE) with a radiative annihilation in a stressed field of uniaxial compression is increased. This fluming effect of own luminescence of crystals at a uniaxial deformation allows searching γ-scintillations, based on own luminescence of excitons, rather than through impurity of a luminescence, as in case of conventional scintillations. In the present work low temperature (at 80 K) influence of uniaxial compression stress on the process of electronic excitations' migration in CsI crystals and mutual transformation of two bands of the radiation of excitons of on- and off- configuration at 4.25 and 3.67 eV respectively has been studied. At X-ray and photoexcitation with an energy of quantum at 5.85 eV, corresponding to the creation of free excitons in CsI crystals, in the spectrum of the radiation at 80 K, two bands with maxima 3.67 and 4.25 eV have been registered. The intensity of the last luminescence in some measurements is dominating, and the impurity luminescence is practically imperceptible. At the photoexcitation with the energy of quantum at 6.45 eV, corresponding to the creation of divided electronic - hole pairs in crystals CsI, in a spectrum of luminescence, except the luminescence at 3.67 eV, impurity luminescence in the range of spectrum 2.0-3.4 eV are found. At such mode of photoexcitation of crystal CsI the contribution of the luminescence at 4.25 eV is small. At low temperature uniaxial deformation (ε=1-2 %) the spectra of luminescence of CsI crystal at all three modes of excitation become identical and consist of one band of luminescence at 3.67 eV. Thus, the uniaxial compression of crystal CsI brings to the redistribution of radiation intensity between 4.25 and 3.67 eV for the benefit of the last with full vanishing of the band of a radiation at 4.25 eV. It is reasonable to connect the effect of vanishing of a radiation at 4.25 eV in intense at 80 K CsI crystals with increase of potential barrier between conditions of on - and off- configurations of self-trapped excitons and it is possible to suppose that at reduction of the symmetry of lattice the on-configuration exciton (3.67 eV) is steady