Luminescence of RbI: Tl

Emission spectra of RbI: Tl for excitation in $A$, $B$, $C$, and $D$ absorption bands were measured at 4.2, 77, and 300°K. At 4.2°K, four prominent bands are observed at 3.42, 4.24, 2.82, and 2.58 eV. The 3.42- and 4.24-eV emission bands appear most prominently for $A$ and $B$ excitations. They are thus assigned $T_{1u}$ and $T_{2u}\to A_{1g}$ transitions, respectively. The 2.82- and 2.58-eV bands appear for both $C$ and $D$ excitations. These are also stimulated with high efficiency in the first exciton region of RbI. Both these bands are attributed to the decay of self-trapped excitons adjacent to thallium ions.