Data and Speculations on the Electronic Problem for the Relaxed ExcitedFCenter

Abstract

The energies of absorption and emission peaks, the lifetime of the relaxed excited state, and the ionization energies of the relaxed excited state of the $F$ center in NaF, KF, RbF, RbBr, and RbI have been studied down to the temperature of liquid He. The low-temperature shapes of the absorption and emission $F$ bands, which have not been previously reported, are also shown. The data on these crystals represent limiting cases from several points of view and allow us to extend considerably the range of the parameters under study. As a consequence, the phenomenology now at our disposition is much more significant and allows us to propose a simple and realistic solution to the problem of the magnitude of ${\tau }_R$. For the situation in which the $F$ center is excited and relaxed, arguments in favor of the $2p$ level being lower in energy than the $2s$ are discussed.