Optical properties of thin films obtained by reactive pulse laser ablation of monocrystalline Si in He, O-2 or N-2 atmosphere have been studied. Both transmissivity and reflectivity of these films were measured in the range of 200-1200 nm and used for a calculation of their optical constants. The analysis of optical spectra has led to conclusion that the films prepared in this manner are composite structures containing at least two phases: the SiOxNy matrix and Si nanocrystallites embedded in it. We have shown good correlation between dependences of visible PL intensity and Si nanocrystallite sizes on preparation conditions.