Undoped and doped polycrystalline Cd0.8Zn0.2S powders with different amounts of samarium (0.01, 002. 0.03, 0.04 and 0.05 M) were synthesized by the controlled co-precipitation technique. Effect of the Sm3+ on structural, elemental, optical and vibrational properties of Cd0.8Zn0.2S: Sm-x samples were investigated. X-ray diffraction (XRD) results showed that the samples prepared were polycrystalline with hexagonal structure. From the XRD patterns, the average crystallite size was calculated it was about 45-90 nm. The band gap of these samples is estimated from the optical absorption studies. The samples showed direct band gap, which varies from 252 to 3.18 eV. Fourier transform infrared spectroscopy (FTIR) showed the characteristic vibrational modes of Cd-S and Zn-S in the wave number range 621-821 cm(-1). Experimental and XRD densities were calculated and analyzed. (C) 2013 Elsevier B.V. All rights reserved.