Optical properties of this ordered defect compound, which crystallized in a chalcopyrite-related structure, were studied by using Raman, optical absorption and photoluminescence techniques. By analyzing the Raman spectra, lattice vibrational modes were identified and possible symmetry assignments were proposed. Optical absorption measurements showed that the band-gap energy, EG, varied from 1.10 to 1.02eV between 10 and 300K. It was found that the variation in EG with temperature was due mainly to a contribution from optical phonons with a characteristic energy of about 0.017eV. The photoluminescence measurements revealed that the main band was due to a donor–acceptor recombination between donor and acceptor levels that had activation energies of 0.050 and 0.025eV, respectively. The phonon energy associated with the Urbach tail, which was higher than that of longitudinal optical phonons, was attributed to the effect of a structural disorder due to deviations from stoichiometry or to cation–cation antisite intrinsic defects. An empirical relationship, previously applied to other ordered defect compounds of the 1:3:5 phase, explained well the variation in Urbach energy with temperature.

Optical Properties of the Ordered Defect Compound CuIn5Te8. C.Rincón, S.M.Wasim, R.Márquez, L.Nieves, G.Marín, E.Hernández, J.Galibert: Journal of the Physics and Chemistry of Solids, 2002, 63[4], 581-9