Plasma enhanced chemical vapor deposition (PECVD) was used to prepare a-Si:H/SiO2 multilayers. Two-step thermal annealing was then used to transform them into nc-Si/SiO2 multilayers. The size of formed nc-Si (about 4nm) can be controlled and room temperature visible photoluminescence was observed from the annealed samples with the peak located at 750nm. Moreover, we found that annealing in hydrogen can enhance the PL intensity of the materials. The electron paramagnetism resonance (EPR) suggested that annealing in hydrogen atmospheye effectively reduces the nonradiative recombination sites existing in the nc-Si and results in the enhancement of the luminescence efficiency.