Transient absorption due to self-trapped excitons in NaBr and NaI

Abstract

Optical transient absorption due to self-trapped excitons (STE's) in both NaBr and NaI crystals has been investigated. Both crystals exhibited optical absorption in a region below 1 eV, peaks of which might be located below 0.23 eV, due to the electronic transitions in the STE. The absorption bands due to the hole transitions appeared at 1.6 and 3.2 eV in NaBr, and at 1.4 and 3.0 eV in NaI, which were very close to those due to the ${\mathit{V}}_{\mathit{k}}$ centers. Absorption bands at 3.2 eV in NaBr decayed with two components, the intensity of which reflected the initial population in the triplet sublevels. These results strongly suggest the ``on-center'' configuration of the STE in NaBr and NaI.