Self-assembled nanocrystals of ZnO were embedded within a SiO 2 matrix by a sequential deposit using reactive R.F. sputtering. The ZnO nanoparticles (NP's) were obtained by depositing a very thin layer (~20 nm) of Zn on the bottom of the valleys of a first SiO 2 rough surface and then covered by another SiO 2 layer at 500 °C. The stress produced, due to the cooling process, by the SiO 2 matrix on the ZnO NP's generates an unusual crystalline phase of ZnO. The crystal structure was determined by means of X ray diffraction patterns. The ZnO + SiO 2 composite shows a transmittance higher than 80 % for wavelengths > 450 nm. Optical absorption allows to reveal the character and value of the optical band gap. Vibrational modes of the material were determined by Raman spectroscopy.