Polaron Theory of Concentration Quenching ofFCenter Luminescence in Alkali Halides

Abstract

Electron transfer rates from excited F centers ( F * ) to nearby ground-state F centers ( F 0 ) via bound polarons are calculated using a semicontinuum model electronic potential in a two-mode coupling. The rate depends on the F * - F 0 separation through the corresponding dependence of the off-diagonal electron-phonon matrix element. Averaging over the F * - F 0 pair separations for a random F center distribution, concentration dependences are derived of intrinsic F center photoluminescent efficiencies in all f.c.c. alkali halides. In particular, the KCl result appears to agree fairly well with experimental concentration-quenching data.