Energy Levels of theFACenter

Abstract

An approximate expression which describes the effects of finite ion size on the $F$-center energy levels is developed and investigated. It is used in a study of the $F_A$-center energy levels; the impurity-induced changes in the ion-size correction, ionic displacements, and polarization are treated as perturbations on the $F$-center energy levels. We find that the splitting of the $F$-center excited state results mainly from the difference in the ion-size correction for the impurity and host cations, and that the approximate $F$-center excited-state wave functions used here concentrate too much charge at the impurity site.