Stoichiometric effects on optical properties of cadmium sulphide quantum dots

Size quantised cadmium sulphide (CdS) nanocrystalline thin films with different particle sizes and stoichiometric ratios were successfully grown on indium tin oxide substrates using an aqueous synthetic route. The effect of cadmium (Cd) to sulphur (S) ratio on the optical properties of CdS nanocrystalline films was investigated using EDAX, UV-vis spectroscopy, photoluminescence and Raman spectroscopy. A satisfactory stoichiometric condition was achieved for 0.13 M concentration of thiourea whereas concentrations in the range of 1-1.2% of mercaptoethanol capping agents produced values much smaller than Wannier exciton diameter for CdS grain sizes, leading to quantum confinement. Photoluminescence emission bands and Raman peaks were analysed for the physical understanding of optimum growth of CdS quantum dots.