Electric-Field Ionization of the ExcitedFCenter in KCl

Following Lüty's original observations that excited $F$ centers could be ionized by applied electric fields, Euwema and Smoluchowski calculated the probabilities for two effects, a low-temperature tunneling effect and a higher temperature Schottky effect. In this paper we extend the Euwema-Smoluchowski theory and report on luminescence measurements of both effects for the KCl $F$ center. The results are analyzed on the basis of the "large-orbit" picture of the relaxed excited state developed by Fowler. The Schottky data fit the theory very well, yielding an effective dielectric constant about equal to the static dielectric constant. The tunneling data are in qualitative agreement with theory.