Polaron Theory of Concentration Quenching of F Center Luminescence in Alkali Halides

Abstract

Electron transfer rates from excited F centers (F^*) to nearby ground-state F centers (F₀) via bound polarons are calculated using a semicontinuum model electronic potential in a two-mode coupling. The rate depends on the F^*−F₀ separation through the corresponding dependence of the off-diagonal electron-phonon matrix element. Averaging over the F^*−F₀ 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.