This paper reports on the synthesis and the electrical, magnetic and optical properties of SmCuOS and SmCuOSe. The magnetic properties reveal that Sm is in its 3+ oxidation state (mu(theo) = g root J(J + 1) = 0.85 mu(B); g = 2/7) with a large Van Vleck contribution, and exclude the possibility of a divalent oxidation state for samarium (Sm2+; F-7(0) state, g = J = 0, mu(eff) = 0). Optical properties were studied by means of diffuse reflectance and photoluminescence spectra in the UV-vis range. The electrical measurements show that the two samarium copper oxychalcogenides, SmCuOSe and SmCuOS are semiconductors with optical band gap (E-g) values of 2.60 and 2.90 eV, respectively. (C) 2006 Elsevier Ltd. All rights reserved.