Optical absorption of glasses in the system (As2Se3)1−xTlx

The optical absorption coefficient (α) has been measured at the absorption edge for three glasses of composition (As2Se3)1−xTl x (x is in the range 0.0–0.7). The values of α were in the range 105–107 cm−1. For the glasses in the system (As2Se3)1− xTlx with the largest values of x there is distinct evidence of an additional absorption mechanism the lower energy. In attempting to explain the origin of this feature we have suggested that for these glasses a sub-band, associated with the presence of thallium, projects into the pseudo-gap at the edge of the valence band; this sub-band may have a tail of states due to compositional disorder. The gamma irradiatin (up to 10 Mrad) has no detectable effect on the optical energy gap.