CdS quantum dots in a polyvinyl alcohol matrix were grown by a chemical method and were characterized by transmission electron microscopy, UV–vis absorption, photoluminescence and energy dispersive X-ray diffraction. transmission electron microscopic studies of CdS films showed that a nearly spherical cluster of CdS quantum dots with an average radius of 10–15nm was formed. From absorption measurements, it was observed that with increasing the polyvinyl alcohol concentration from 5 to 8wt%, the absorption edge shifts from 3.1 to 3.6eV, which was attributed to an increase in quantum confinement with decreasing the quantum dot size. Photoluminescence studies in an energy range of 1.8 to 3.3eV showed two distinct peaks. The higher-energy peak corresponds to band edge emission, whereas the lower-energy peak corresponds to defect emission. Energy dispersive X-ray diffraction results revealed that the atomic concentration of cadmium was much lower than that of sulphur, indicating that cadmium vacancies were predominant. It was concluded that cadmium vacancies were mainly responsible for defect emission in the photoluminescence spectrum.

The Effect of Cadmium Vacancies on the Optical Properties of Chemically Prepared CdS Quantum Dots. S.Madan, J.Kumar, I.Singh, D.Madhwal, P.K.Bhatnagar, P.C.Mathur: Physica Scripta, 2010, 82[4], 045702