Luminescent a-Si:O:C layers were obtained by magnetron co-sputtering and annealing. The maximum photoluminescence intensity is comparable with that of porous silicon. The luminescence maximum is between 1.8 eV and 2.2 eV, X-ray photoelectron spectroscopy finds both C-Si and C-C bonding and maximum luminescence is obtained when the amount of the two kinds of bonding is comparable.