Electronic structure of thallous centres and Tl⁺ - V_k recombination in KCl crystal

Parameters of impurity Tl ion required for the calculation of different thallous centres in alkali halides are obtained for the semiempirical method of the intermediate neglect of differential overlap (INDO). The electronic structure of Tl⁺, Tl²⁺ centres in KCl is calculated. The potential energy curves for the recombination of nearest Tl⁺, V_k centres against the breathing vibrational mode of the V_k centre are calculated. This recombination (hole trapping) is found to be nonradiative tunneling with small activation energy rather than radiative one. A number of experimental data is also discussed in the light of the present calculations.