Lifetime ofFAandFHcenters in alkali halides

The lifetime data on the $F_A$ and $F_H$ centers, the latter obtained and presented here for the first time, show a substantial difference in the perturbations induced in the $F$ center by the foreign ion in the two cases. For the $F_A$ center, both excited in the $F_{A_1}$ and $F_{A_2}$ absorption band, we have ${\tau }_R\left(F_{A_1}\right)\equiv {\tau }_R\left(F_{A_2}\right)$; in the case of $F_H$, ${\tau }_R\left(F_{H_1}\right)\ne {\tau }_R\left(F_{H_2}\right)$. The $F_A$ and $F_H$ data are discussed with particular reference to relaxed-excited-level structure.