Abstract
In recent years a large amount of activity has been carried out searching for novel or advanced materials which exhibit large nonlinear third-order susceptibility 
. Emphasis has been put on materials suitable for integrated optical circuits, since the guided-wave format can provide additional routes to the conception and realization of photonic devices. The preparation of nanoparticle-doped glass by the sol - gel technique represents one of the most promising approaches: here we give a short overview of alternative processes to control the size of semiconductor clusters and we present experimental results from CdS- and PbS-doped silica - titania sol - gel films.