Luminescence and F-H Pair Creation from Self-Trapped Excition in KCl:I, RbCl:I and KCl:Br

The electronic structure of various types (one-center, two-center, and dimer complex) of self-trapped excitons (STE's) in alkali halide crystals containing heavy halogen impurity atoms, has been studied by the extended-ion method (developed earlier for STE's in pure alkali halides) coupled with a CNDO code. Results of the calculations for KCl:I, RbCl:I, and KCl:Br are generally in satisfactory agreement with experiment. In particular, two distinct configurations have been found for the two-centre type STE's, which accounts for the blue and the blue-green emission bands. A general discussion of defect (F-H pair) formation mechanism in these systems, consistent with experimental observations, has also been presented.