Si nanograins embedded in silicon oxide matrix have been obtained by thermal annealing at 1100°C during one hour, either after implantation of Si+ into thermal SiO2 layers or after magnetron cosputtering of both Si and SiO2. The spectral distribution of the photoluminescence (PL) in both systems is similar and peaks in the red visible region (1.45–1.60 eV). The results obtained indicate that for high PL efficiency, the films have to be annealed at temperatures high enough to achieve phase separation. This was observed from the gradual shift of the infrared bands of the silica matrix toward those of thermal SiO2, together with the appearance of the crystalline silicon Raman vibrational mode in the spectra. The similar behavior of samples obtained by ion implantation and by sputtering suggests a more complex origin of the PL than quantum confinement.