Tunable Visible-Light Emission from CdS Nanocrystallites Prepared under Microwave Irradiation

Abstract

The microwave (MW)-assisted reaction of cadmium acetate with thiourea in N,N-dimethylformamide (DMF) was controlled by controlling the MW irradiation time in the presence of 1 -thioglycerol as a capping agent. The peak position of the absorption band of the CdS nanocrystallites, dispersed in chloroform, shifts toward longer wavelength with increasing MW irradiation time, indicating growth of particle size under prolonged MW irradiation. However, the peak position of absorption band remains at the same wavelength, and only the intensity of the absorption band is increased when the MW irradiation of the colloidal solution of CdS nanocrystallites in DMF is periodically interrupted, keeping the solution at room temperature (27 °C) before each irradiation. This suggests that the particle growth occurs only during the continuous irradiation of MW and stops when the system is cooled down. From the spectral absorption edge, the diameter of CdS nanoparticles has been estimated. Photoluminescence of the CdS nanocrystallites, dispersed in chloroform, observed in the visible range shifts toward higher wavelength with increased duration of MW irradiation. When the MW irradiation was repeated for a fixed duration in colloidal solution of CdS nanocrystallites in DMF, enhancement in PL intensity was noticed without any change in the emission peak position. The relative PL quantum yield of the CdS nanocrystallites was estimated under various experimental conditions. Time-correlated single-photon counting experiments were performed to study the time-resolved photoluminescence of CdS nanocrystallites. The observed emission decay profiles have been simulated by using the multiexponential model.