Single crystals of the CuIn5Se8 compound have been synthesized by the directed crystallization of the melt in a single-zone furnace (vertical Bridgman variant), starting from the stoichiometric mixture of constituent elements. Phase purity of the synthesized material was confirmed by powder X-ray diffraction. Transmittance as a function of wavelength was recorded in the wavelength range of 0.5-2.500 mu m at different temperatures. Band-to-band transition energies were calculated from the transmission spectra in the region of the fundamental absorption edge. From the energy gap E-g temperature dependence the Debye temperature Theta(D) = 215 +/- 8 K was deduced. The photoluminescence spectra of the CuIn5Se8 crystals were detected in the temperature range from 10 to 300 K at various powers of laser excitation. The spectra exhibit emission band localized at 1.00eV which can be attributed to the donor-acceptor-pair recombination. (c) 2006 Elsevier B.V. All rights reserved.