Preparation of CdS-doped glasses by the sol-gel method

Abstract

CdS-doped Si02 glasses have been prepared through the sol-gel process. A methanol solution of cadmium nitrate and thiourea in a molar ratio of 1:2 was added to the Si02 sol prepared from silicon tetraethoxide. The mixed solution was left for gelation at 50 °C and thereby complexes of cadmium nitrate with thiourea were confined in the gel. The gel obtained was then heat-treated at 350 °C in air for the decomposition of the complexes to CdS, the elimination of residual organics, and the densification. The above process produced the transparent Si02 glasses doped with CdS microcrystallites up to Cd/Si = 0.05. The optical absorption edge of the CdS-doped glasses moved to longer wavelengths from that of non-doped Si02 glasses with increasing Cd/Si ratio. The size of CdS microcrystallites in the glasses was further controllable with the additional heat-treatment at around 400°C in a lO H2S/90% Ar stream. For these CdS microcrystallite-doped glasses, the peak of photoluminescence was shifted to shorter wavelengths relative to the absorption edge of CdS crystal, in agreement with the blue shift of the optical absorption edge; these shifts were indicative of the quantum size effects.