Silicon-based light emitting device is the missing piece in the design of complete optoelectronic circuits on silicon. A complete electrical and optical characterization of electroluminescent silicon-nanocrystals based devices is presented. This characterization is the first step in the design of coupling structures with optimal injection of light into optical waveguides, which will allow the development of all-silicon photonic circuits. In this paper, a novel coupling structure based on rectangular surface grating has been studied with promising results, increasing the coupling efficiency to SU-8 waveguides up to 25 times. The SU-8 photoresist is fully compatible with silicon technology and can be used to define waveguides as well as microfluidics channels. These properties are interesting for the final application of the present study, which is to obtain a Lab-on-a-chip device, integrating all the optical elements, control electronics and microfluidics channels.