Silicon nanostructures embedded in an amorphous matrix have been synthesized by Pulsed Laser Deposition (PLD) at room temperature. The structural and optical properties of the materials were tailored by varying deposition parameters; attention has been devoted to the nanoscale morphology of the Si layers which has been varied from compact to open-porous by changing background gas (Ar) pressure (1-100 Pa). An adopted simple-minded strategy of a compact Si layer deposited on top of nanostructured layers showed to reduce quite successfully ex-situ oxidation. Raman spectroscopy suggests that as deposited samples are mainly constituted by amorphous silicon with nanocrystals (NCs) inclusions. The results indicate that the average size of the Si NCs varies in the range 2-6 nm. Photoluminescence (PL) responses are found to be strictly dependent on morphology and strengthen up the idea of the quantum confinement effect in the obtained nanostructured material. The results are interpreted in terms of particle size distribution, crystallinity and partial surface oxidation of the silicon nanostructures.