A novel method for the fabrication of nanometer-sized Si crystals in an amorphous SiO2 matrix by ion implantation and thermal processing is reported. Transmission electron microscopy indicates the formation of Si nanocrystals by annealing at 1 100 degrees C, and the growth in average size of Si nanocrystals with increasing annealing time. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time, while the excitation spectrum of photoluminescence increases as the photon energy increases and its shape depends on annealing time. The results indicate that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not dire to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO2. This method is fully compatible with silicon microelectronic technology.