The relationship between the photoluminescence (PL) intensity due to the W (orI1) center and the oxygen concentration in implanted silicon crystals was studied. The PL intensity of the W center decreased consistently with increasing oxygen concentration for carbon-implanted samples with a wide range of carbon fluences, while it showed no dependence on the oxygen concentration for samples implanted with elements such as hydrogen, silicon, and heavy metals. Based on these results and considerations of the reactions of intrinsic defects generated by implantation, the origin of the PL W center was attributed to a defect composed of silicon self-interstitials. ©1998 American Institute of Physics.