Semiconductor nanoclusters embedded in thin coatings of transparent and homogeneous silica glasses are suitable materials for the development of optical devices. The optical properties of such systems are strongly dependent on the elemental composition and the morphology of the coatings as well as on the nanocluster size distribution, their mutual interactions and the interactions with the host matrix. To achieve a good control over film composition and morphology the sol-gel route was used. The sol-gel synthesis. of ZnO nanocrystals embedded in silica has been faced by the study of the gel-derived binary system ZnO-SiO2. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OC2H5)(4), TEOS] and zinc acetate [Zn(CH3,COO),(2)] was adopted. Zinc oxide nanograins have been generated in silica by hydrolysis of TEOS and the zinc salt and subsequent thermal annealing of the coatings. The system evolution under thermal treatment was studied by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, UV-Vis absorption spectroscopy and secondary-ion mass spectrometry.