On the conditions of synthesis of nanocrystalline cadmium sulphide (CdS) particles by an emulsion technique

Abstract

Nanocrystalline CdS particles with a size range of 8-30 nm and mean size of about 14 nm were synthesized following an water- in-oil type emulsion technique at 80° ± 1°C under mechanical agitation and sonication. An ionic impurity-free nonionic surfactant of high hydrophilic-lipophilic balance (HLB) value of 15, i.e., polyoxyethylene sorbitan monooleate (Tween 80), was used as the emulsifying agent. The effects of Cd²⁺ ion concentration, mechanical agitation, sonication and calcination temperature on particle formation were examined. The synthesized particles were characterized by transmission electron microscopy (TEM), particle size analysis, X-ray diffraction (XRD) and photoluminescence (PL) study. TEM indicated the formation of nanosized particles. In the absence of mechanical agitation during particle formation, submicrometre-sized particles with a bimodal distribution were noticed, while in the absence of sonication, larger particles of mean size 49 nm were developed. Cubic CdS peaks were identified by XRD in the synthesized powders. XRD also indicated the crystallite size of about 3 nm in the as-prepared CdS particles. The crystallite size increased with the increase in calcination temperature and Cd²⁺ ion concentrations. Photoluminescence spectra of different samples indicated that with increasing concentration of Cd²⁺ ions surface defect states are reduced.