The transient absorption spectrum of the self-trapped exciton (STE) localized at an iodine dimer (${\mathrm{I}}_2^{\mathrm{-}\mathrm{-}\mathrm{*}}$) in an iodine-doped KCl crystal (KCl:I) has been investigated at 80 K. The absorption band due to the electronic transition was found around 0.36 eV, and the bands due to the hole transitions around 1.5 to 3.0 eV. The electronic transition band occurred in an extremely lower-energy region than that of the STE in KI or RbI crystals, suggesting the ‘‘on-center’’ configuration of the STE (${\mathrm{I}}_2^{\mathrm{-}\mathrm{-}\mathrm{*}}$) in KCl:I.

• Received 12 July 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.3283