Since the discovery of strong visible photoluminescence (PL) at room temperature from porous Si done by Canham in 1990, 1 the possibility to obtain efficient light emission from Si nanostructures has attracted the efforts of a wide scientific community. Very rapidly the focus of the research moved from the brightly-emitting, but brittle and unstable, porous Si to Si nanocrystals (Si-nc) embedded in SiO2 films. Si-nc exhibit a remarkably higher stability (both from mechanical and optical point of views) with respect to porous Si and are fully compatible with the technology used for Si-based microelectronics with regard to the techniques used for their synthesis (chemical vapor deposition, sputter deposition, ion implantation) and processing (conventional dry and wet etching processes are easily applicable for the patterning of SiO2 layers containing Si-nc). The efforts done by several research groups have led to a deep comprehension of the complex phenomena ruling the process of light emission from Si-nc and to the optimization, in terms of efficiency and stability, of their properties. 2-11 A major advancement has been represented by the discovery that Si-nc can exhibit optical gain, 12-15 so opening the route towards the development of a Silaser. It is generally recognized that the unusual properties of Si-nc are tightly connected to the very stable passivation ensured by the surrounding SiO2, mainly by eliminating dangling bonds through the formation of Si= O bonds; 16 furthermore, the SiO2 matrix in which the nc are embedded constitutes also a low defect density medium in which the efficiency of nonradiative recombination processes is strongly …