We present in this paper a systematic study of the evolution of photoluminescence (PL) emission of Si nanocrystals embedded in SiO2 with elaboration conditions. Si nanocrystals have been synthesized in SiO2 by ion implantation with doses that cover from 1 x 10(16) to 10(17) ions/cm(2). This corresponds to a Si super-saturation of 1-10 at.% at the projected range. The annealing process was performed at 1100 degreesC. These samples show a wide (0.26 eV) and very intense PL emission centered at about 1.72 eV. The intensity of this emission shows a typical behavior with annealing time, with a fast transitory increase that bends over to reach asymptotic saturation. There is a linear increase of the PL intensity with the implantation dose at this saturation stage. The structural characterization has been performed by transmission electron microscopy and electron spin resonance. Based on these results, the kinetic evolution of the volume fraction of precipitates and their surface rearranging have been correlated with the time evolution of PL intensity. The band gap of nanocrystals has been determined to be 1.85 eV from PL excitation measurements. All the results indicate that the radiative recombination process is related with recombination at a Si-O bond of nanocrystal-matrix interface, together with the emission of a phonon (a local vibration of the Si-O bond).