Electronic Structure of the Exciton

I. Localized Exciton in KCl

Abstract

The present situation of the exciton problem is discussed briefly. The localized excitons of KCl in both optical and X-ray absorption have been worked by using Wannier-Slater’s equation for the perturbed lattice, which may be considered to essentially correspond to the quantum-analogue of von Hippel’s semi-classical model of the exciton. The perturbing potential fields in Wannier-Slater’s equation are evaluated numerically by the use of Hartree’s data and then the best-fit analytical functions are constructed with fair accuracy. The solutions of the equation are worked by the variational method. The result for the optical exciton is observed to be in fair agreement with the experiment. As for the X-ray exciton, the quantitative comparison with our results can hardly be carried out at present, since the position of the bottom of conduction band can not be measured accurately on the X-ray absorption spectra. On the basis of our results for X-ray exciton, however, some discussions on the characteristic structure near the absorption edge in KCl are presented.