CdS nanoparticles and sol-gel process

We present two approaches for the sol-gel synthesis of transparent solids in which CdS nanoparticles are homogeneously dispersed. In any case CdS nanocrystals are obtained by precipitation either in reverse micelles or in the presence of a complexing thiol. The grafting of the 4-fluorothiophenol at the surface of the particles leads to highly concentrated colloids in acetone. In a first approach, CdS/silica nanocomposites are prepared introducing this concentrated CdS colloid in a silica sol which contains 3-mercaptopropyltrimethoxysilane to ensure the homogeneity of the CdS dispersion. The luminescence properties of the materials are improved by using methyltriethoxysilane instead of tetraethoxysilane as the alkoxide precursor of the silica matrix. Further increase of the luminescence efficiency is also observed if a single Mn2+ ion is present inside the CdS particle. In a second approach, pure CdS nanocristalline materials (bulk or thin films) are obtained from the sol-gel processing of the concentrated colloids stabilized by 4-fluorothiophenol. The mechanisms driving the aggregation of the particles and the gelation of the system are explicited. Thin films as well as monoliths can be produced. The general principles of this method are not restricted to chalcogenide materials, and should therefore enlarge the applications of the sol-gel process to other nonoxide materials.