Today electronics is almost totally based on Silicon, but its optical properties are quite mediocre. To build silicon nanostructures in form of porous networks or of nanocrystals allows obtaining emission proprieties in the visible, which are particularly interesting for applications in optoelectronics. We are interested in optical amplification processes in silicon nanocrystals and measure in particular their gain. The final aim is to obtain an efficient material for the fabrication of laser sources, integrated into the electronic device