The formation of CdS nanocrystals in silica gels by gamma-irradiation and their optical properties

Silica gels dispersed with nanoscale CdS particles were prepared by the sol–gel process combined with γ-irradiation at room temperature and in ambient pressure. X-ray diffraction (XRD) and transmission electron microscopy have revealed the existence of CdS nanocrystals, as well as their structures and size distributions. The silica matrix affects the crystal structure of the CdS particles produced. A prominent quantum size effect was observed through the absorption and luminescence spectra of samples irradiated for different periods of time. The most interesting phenomenon is that on increasing the irradiation time, the surface-state emission disappears, and simultaneously band edge emission appears and becomes even stronger with longer irradiation: this is thought to be due to the passivation effect by the surrounding matrix through the interface electrostatic interactions around the particles.