Electronic structure of the self - trapped sodium chloride exciton in

The electronic structure of the relaxed exciton in sodium chloride is investigated using a Hartree-Fock method. The model concentrates on a cluster of two sodium and two chlorine ions surrounded by an array of point charges. The excited states of the exciton and the associated transitions are discussed. The results are compared with experiment and with the phenomenological models proposed by earlier workers. A number of features are confirmed, giving a general picture close to that of Kabler and his co-workers. One problem emerges, since it proves possible to understand the U luminescence or the n luminescence, but not both at present. Possible reasons are discussed. In other respects. there is good agreement with experiment, especially for the optical transitions starting from the lowest triplet state of the exciton.