We studied the photoluminescence (PL) of Si nanocrystals (Si-NCs) embedded in SiO2 obtained by ion implantation at MeV energy. The Si-NCs are formed at high depth (1-2？μm) inside the SiO2 achieving a robust and better protected system. After metal ion implantation (Ag or Au), and a subsequent thermal annealing at 600°C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. The ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs) could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO2 matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensified. We have selected different atmospheres (air, H2/N2 and Ar) to study the relevance of these annealing gases on the final PL from Si-NCs after metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation. 1. Introduction A common process used to obtain silicon nanocrystals (Si-NCs) involves ion implantation of Si ions into silica matrix followed by thermal annealing. Precipitation of excess Si in SiO2 typically requires temperatures in the range 1000–1100°C for 1？h and produces Si-NCs with diameters between 3 to 7？nm [1, 2]. Si-NCs exhibit a strong room temperature photoluminescence (PL) as a direct consequence of their small size, but nonradiative surface defects, as Pb defect, compete with radiative process [3–6]. SiO2 is an appropriate matrix for Si-NCs since it can passivate some dangling bonds that can cause nonradiative transitions. However, a better control of surface defects on Si-NCs is valuable for light-emitting applications [3, 6, 7]. Annealing in molecular hydrogen can reduce the high concentration of surface defects, and then luminescence intensity from Si-NCs significatively increases [2–8]. It has been reported that a sample containing Si-NCs and passivated at 510°C in molecular hydrogen can increase its photoluminescence signal by a factor of seven [4]. Si ion implantation is typically done at energies in the range of 35–400？KeV so the formed nanocrystals are inside the silica matrix but near its surface at a distance not exceeding 1？μm [1–4, 6, 8–11]. So molecular
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