Experimental spectra for copper gallium (indium) ternary selenides (tellurides) crystals, measured in the 50-500 cm(-1) frequency range, revealed four infrared-active modes. Spec tral dependencies of refractive index and absorption coefficient were computed from reflectivity experiments. The frequencies of optical modes, damping constants and oscillator strengths were also evaluated. The bands observed in IR spectra were provisionally attributed to various vibration types (valence and valence-deformation). Crystal structure and atomic composition ratio of the constituent elements in Cu3Ga5Se9, Cu3In5Se9 and Cu3In5Te9 crystals were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy. (C) 2017 Elsevier GmbH. All rights reserved.