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The effect of uniaxial stress applied at various temperatures along the 100 crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for pure and Tl + , Na + -containing KI and RbI crystals under excitation in the exciton and band-toband absorption region as well as under x-ray excitation. An increase of the intrinsic/extrinsic emission intensity ratios has been observed and explained by the stress-induced (i) enhancement of the self-trapping efficiency of electronic excitations and the decrease of their migration length and (ii) suppression of the nonradiative decay of excitons into stable radiation defects. A strong influence of the uniaxial stress on the structure of the STE adiabatic potential energy surface has been detected in RbI which is evident in the stress-induced increase of the E x /π and, particularly, of the σ/E x emission intensity ratios. This effect has been connected with the increase in the energy barriers between various STE configurations in the compressed crystal lattice. The dependence of the on-centre STE emission intensity in alkali halides on the distance between the nearest lattice anions and on their size has been discussed.

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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.