Organically modified silicates (Ormosils) have been used as the matrix material in the preparation of several different kinds of nanocomposites for optical applications via the sol-gel method. Polydimethylsiloxane (PDMS) and dimethyl-phenylmethylsiloxane copolymer have been used as the organic components to modify SiO2 network in the Ormosils. A broad range of optically active materials such as semiconductors, metals, oxides, organics, and ions have been incorporated into Ormosils. The preparation process for the photo-active material doped Ormosils is described. The dependency of Ormosil properties on processing parameters and the effects of organic modifications on the silica network are investigated. Some examples of using Ormosils derived from tetraethoxysilane and PDMS as matrices to prepare photo- active composite materials are reported. Ormosils proved to be a promising new class of materials for various optical applications.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.