We all know that due to its indirect band-gap, silicon is not a suitable semiconductor to manufacture optoelectronics. Having a Silicon light source (LED or LASER) though, would come in very handy in today's technology, especially in telecommunications. There is a decade or so that electroluminescence and photoluminescence have been observed from porous Silicon. Reseach has been re-stimulated quite recently when initially photoluminescence and later electroluminescence was observed in structures containing Silicon nanocrystals. Contrary to porous Silicon, silicon nanostructure devices ARE FULLY compatible with today's CMOS processes. This means that the cost of combining the drive electronics (silicon) and light source (composite semiconductors) is practically eliminated, allowing in a few years the full integration of these two components and other optics as well (waveguides, modulators, etc.) to be possible, giving a new direction in the evolution of electronics. ST has already produced a LED based on Er-ion doped Si nanocrystals. A nice presentation of the subject, is by Intel here:http://www.intel.com/technology/itj/2004/volume08issue02/art06_siliconphoto/p01_abstract.htm
and you may as well perform a google serach, you'll find many relevant pages.