A detailed analysis of the optical properties of silicon rich oxides (SRO) thin films and the factors that influence them is presented. SRO films with different Si content were synthesized via LPCVD (low pressure chemical vapor deposition) on sapphire substrates. Photoluminescence (PL), UV/Vis and Raman spectroscopy were used to characterize the samples. An intense emission in blue region was found. An interesting fact is that the optical band gap correlates linearly with the reactants ratio, which allows the tuning of the band gap. The influence of parameters such as substrate, Si content, annealing temperature and annealing time on the optical properties are discussed and the possible mechanisms of the photoluminescence are compared with our experimental data.523212218Deutsche Forschungs GemeinschaftCONACyT