Quantum confinement effects of CdS nanocrystals in a sodium borosilicate glass prepared by the sol-gel process

Abstract

Experimental evidences of both weak and strong confinement regimes are reported on CdS nanocrystals embedded in a sodium borosilicate glass matrix. A method, based on the sol-gel technique, is used for the preparation of CdS-activated glass. This route is capable of providing nanocrystals covering a wide range of radii with small size dispersion. Low-temperature linear-absorption spectra have been analyzed in terms of excitons and electron-hole confinements by fitting the results of a numerical calculation to experimental findings. The model used, in the envelope-function formalism, involves both a Lorentzian broadening of the exciton energy states inside each nanocrystal and a Gaussian size distribution. The improvement of crystal quality and the sharpening of the size distribution by thermal annealing is also studied versus both time and temperature of treatment. It is shown that we can keep a tight control on the crystallinity, average size, and size distribution of the nanocrystals by rather simple adjustments and short treatments.