SELF-TRAPPED EXCITON LUMINESCENCE IN KBR1-XIX AND RBBR1-XIX SOLID-SOLUTIONS

Emission spectra and decay characteristics of luminescence in KBr1-xIx and RbBr1-xIx solid solutions have been investigated in the whole range of composition x. The emission band due to localized excitons at I- dimer centers in bromides, which consists of singlet and triplet components, is found to connect continuously with intrinsic sigma-band in pure iodides. The triplet component of the band is transformed into another emission with larger Stokes-shift in the intermediate region of x. Time-resolved studies on this emission in KBr1-xIx have clarified that it consists of two triplet emission bands differing by approximately 0.2 eV in their peak energies. The lower energy one corresponds to pi-band in KI. We demonstrate that the relaxed exciton configurations of different types are selectively realized depending on the local environment surrounding the I2- molecular core of the exciton. Discussion is given on the dynamical relaxation process of free excitons in iodides.