Semicontinuum vibronic model of theFcenter

Abstract

The semicontinuum model of the $F$ center is extended to include vibrational coupling. The promoting mode for a number of transitions undergone by the $F$ center is assumed to be of $A_{1g}$ symmetry. A configurational coordinate diagram of the NaI $F$ center is calculated. Two radiative deexcitation channels are predicted, starting from the relaxed excited $F$ and bound polaron states, respectively. The $F^{*}$-polaron transition occurs via a nonradiative process involving nuclear tunneling at low temperature. The model agrees reasonably well with recent experiments.