We investigate the dependence on the interionic distance R of the transition energy ΔE of the electron from 1s to 2p states of the self-trapped exciton (STE) for alkali halides. It is found that the ΔE-vs-R plots, except for NaBr and NaI, fall in two distinctive straight lines, showing that the STE in alkali halides can be divided into two groups. This grouping is found to be in accordance with the grouping in terms of the Stokes shift presented by Kan’no, Tanaka, and Hayashi. The relaxed configuration of excitons in alkali halides has been discussed on the basis of these results.

• Received 13 August 1991

DOI:https://doi.org/10.1103/PhysRevB.45.1432