Temperature dependence of the indirect bandgap in thallium bromide from cathodoluminescence spectroscopy

The temperature dependence of the indirect bandgap in thallium bromide has been determined using variable temperature (5 K to 300 K) cathodoluminescence. The spectra include transitions associated with both the indirect (2.66 eV at 5 K) and the direct (3.0 eV at 5 K) bandgaps. Least-squares analysis has been used to obtain fitting parameters for three analytical models commonly applied to describe the dependence of the bandgap on temperature for the lowest energy indirect transition. The indirect bandgap emission shifts to an energy of 2.86 eV at 300 K. We find a significant difference in the behavior of the luminescence associated with the direct bandgap, which does not appear to shift to the extent predicted by earlier measurements of the exciton absorption edge.