Vibronic Theory of the Stark Effects on the Relaxed Excited State of the F Center

Abstract

The \(\varGamma^{-}_{4}\)-mode phonon interaction in the relaxed excited state (RES) of the F center has been investigated through a theoretical study of the Stark effects on the RES, as an extension of the Kayanuma and Toyozawa theory. The general expressions of the temperature dependence of both the Stark polarization P ( T ) and the radiative life time τ( T ) are derived. They include two parameters; 2 s -2 p electronic energy difference Δ , and \(\varGamma^{-}_{4}\)-phonon coupling constant S 1 . These parameters are determined by theoretical curve-fitting of the experimental data of P ( T ) for potassium and rubidium halides. They give a consistent explanation of τ( T ) for KF, KCl, KBr, and RbCl, and also give the values of the other important parameters of the RES. It is concluded that, in the RES, Δ ≥0; this implies that the 2 s state lies either below the 2 p states or degenerates with them before introducing the electron-phonon coupling.