In this paper, silica thin films with different CdS quantum dot concentrations are deposited on glass substrates by a sol-gel dip-coating process, followed by thermal treatment at different annealing temperatures. The effects of CdS concentration and annealing temperature on the structural and optical properties of the composite films are investigated through X-ray diffraction, UV-Vis spectroscopy and photoluminescence spectra. Results show that the CdS crystallites with diameter of several nanometers in silica matrix are in cubic phase and shows preferred orientation of (200). The Stokes shift of about 0.3eV between its absorption peak and emission peak makes the CdS composite film be possible as an efficient light shifter to solar cells.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.