Effect of uniaxial stress on luminescence of undoped and thallium-doped KIand RbI crystals

The effect of uniaxial stress applied at various temperatures along the [10 0] crystal axis on the self-trapped exciton (STE) and impurity-induced lumi nescence has been studied for pure and T1(+), Na+-containing KI and RbI cry stals under excitation in the exciton and band-to-band absorption region as well as under x-ray excitation. An increase of the intrinsic/extrinsic emi ssion intensity ratios has been observed and explained by the stress-induce d (i) enhancement of the self-trapping efficiency of electronic excitations and the decrease of their migration length and (ii) suppression of the non radiative decay of excitons into stable radiation defects. A strong influen ce of the uniaxial stress on the structure of the STE adiabatic potential e nergy surface has been detected in RbI which is evident in the stress-induc ed increase of the E-x/pi and, particularly, of the sigma/E-x emission inte nsity ratios. This effect has been connected with the increase in the energ y barriers between various STE configurations in the compressed crystal lat tice. The dependence of the on-centre STE emission intensity in alkali hali des on the distance between the nearest lattice anions and on their size ha s been discussed.