Temperature dependence of dielectric function and optical transitions in TlInSe2 and TlGaTe2

Abstract

The principal components of the dielectric function of TlInSe2 and TlGaTe2 crystals with quasi-one-dimensional chain structure have been studied over the photon energies 1.5–5.0eV in the temperature range 140–400K, with due regard to the reported phase transitions. For TlGaTe2, the absolute values of the dielectric function experience a sudden temperature-induced change at 290K in nearly all the accessed photon energy range. The energy and other parameters of the critical points for inter-band optical transitions related to the obtained dielectric function have then been retrieved for both TlInSe2 and TlGaTe2. An abrupt change in the energy of the critical point, positioned at 2.93eV at room temperature and formed by optical transitions induced by the light polarized along the chains, has then been disclosed for TlGaTe2 at 290K.