The optical properties of bulk Silicon are deeply modi ed if the material isrnmanipulated at the nano metric size. In particular the growth of nanocrystallinernSilicon(nc-Si) structures constitutes today a promissing approach for the develop-rnment of Silicon based light emitting devices. In this thesis the in uence of quantumrncon nement on the optical properties of nc-Si is investigated.We basically concen-rntrate on the Photoluminescence (PL) of nc-Si. One of the fundamental parametersrndescribing The PL mechanism of nc-Si is the radiative recombination rate. In orderrnto examine the mechanism of the PL from the nc-Si the optical transition and thernradiative transition rate are studied based on the quantum con nement(QC)model.rnWe nd that the radiative recombination rate varies as . Where d3À€€ is the diame-rnter of the spherical crystallites. This result shows that the radiative recombinationrnrate increases with decreasing the size of the nc-Si. As a result, the PL emissionrnintensity enhanced due to QCE and the PL can be tuned into the visible range