Self-Trapped Exciton Luminescence in KBr1-xIx and RbBr1-xIx Solid Solutions

Emission spectra and decay characteristics of luminescence in KBr 1- x I x and RbBr 1- x I x 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 σ 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 KBr 1- x I x have clarified that it consists of two triplet emission bands differing by ∼ 0.2 eV in their peak energies. The lower energy one corresponds to π band in KI. We demonstrate that the relaxed exciton configurations of different types are selectively realized depending on the local environment surrounding the I 2 - molecular core of the exciton. Discussion is given on the dynamical relaxation process of free excitons in iodides.