In the last decades, in the field of silicon microphotonics many efforts have been made to find strategies in order to obtain efficient luminescence from silicon or from Si compatible materials that could be totally integrated on Si microchips. Among the several approaches, mixed rare earth silicates and oxides have received great attention as active media, owing to their compatibility with the standard Si technology and the possibility to dissolve inside high concentrations of luminescent centers. In this paper we will review the last achievements on the investigation of the structural and optical properties of erbium doped yttrium silicates and oxides. We will further show the advantages of using bismuth as Er co-dopant, as strategy to improve optical efficiency at 1540 nm, wavelength of interest for telecommunications. The stabilization and the role of the Bi3+ oxidation state will be evidenced along the paper by comparing …