SELF-TRAPPED EXCITON LUMINESCENCE IN MIXED K1-XRBXI CRYSTALS

The self-trapped exciton (STE) luminescence of mixed K(1-x)Rb(x)I crystals has been investigated by using D2 lamp and synchrotron radiation as light sources at 11 K. The results show that the sigma-emission band is kept well over the whole composition range, and its decay time changes continuously from 2.0 ns in KI to 4.1 ns in RbI. It is found that the virtual-crystal model is quite valid for the singlet STE state which is responsible for the sigma-luminescence. The pi-emission band of KI is closely connected to the E(x) band, not the pi-band, of RbI with increasing x. The pi-band of RbI disappears in the region x < 0.4. These facts are compatible with a recent theoretical model indicating that at equilibrium the lowest triplet STE is situated off-center. A brief discussion of the exciton relaxation into STE states in alkali halides is presented.