Self-trapped excitons and F centers were considered in terms of the extended-ion approximation. It was found that the self-trapped exciton was a nearest-neighbor F-H pair with C1 symmetry. Theoretical predictions of the spectra of the self-trapped excitons and F centers were in good agreement with experiment. Stable F-H pairs which converted from self-trapped excitons were generated only at the hole excited state of the self-trapped excitons, according to calculations of the adiabatic potential energy curve of the self-trapped excitons plus F-H pairs.

L.F.Chen, L.Zhou, K.S.Song: Journal of Physics - Condensed Matter, 1997, 9[31], 6633-42