Stability and optical properties of self-trapped exciton in alkali halides

A simple small-polaron model of the V k centre and the self-trapped exciton (STE) in alkali halides with NaCl-type structure is presented. First, the stability of the V k centre is discussed. On the basis of this result, it is shown that the electron in STE can be described by the effective mass equation including the electron-phonon interactions. Solving the equation by the variational method, the authors discuss the mechanism of stability of the STE and calculate the transition energies of the transition absorptions and the pi luminescence. Satisfactory agreement with experiment has been obtained for both of them in nine alkali halides.