Fundamental absorption edge of TlSe and TlInTe2 crystals

Experimental results are presented on the absorption edge of TlSe and TlInTe2 crystals in the temperature range 4.2 to 300 K in two geometries, E-vector parallel to C-vector and E-vector perpendicular to C-vector. The temperature behavior of the band gaps for direct and indirect transitions has been studied. An attempt is made to give a theoretical description of the peculiarities observed in the absorption spectra at low temperatures within the framework of the exciton absorption mechanism