Study of Quantum Yield and Photoluminescence of Thiol Capped CdS Nanocrystallites

Abstract

For the preparation of thiol capped CdS nanocrystallites, the microwave (MW) assisted reaction of cadmium acetate with thiourea in N, N‐dimethylformamide (DMF) was controlled in the presence of two capping agents, 1‐butanethiol and 2‐mercaptoethanol. The peak position of the absorption band of the CdS nanocrystals in DMF solution shifted towards longer wavelength with increasing duration (by repeated exposure for a fixed time) of MW irradiation, for 1‐butanethiol caped CdS nanocrystals indicating growth of particle size. However, the peak position of absorption band remained nearly at the same wavelength and only the intensity of the absorption band increased with increasing duration of MW irradiation for the 2‐mercaptoethanol capped CdS nanocrystals. Photoluminescence (PL) of the CdS nanocrystals in solution with 1‐butanethiol as capping agent was observed to shift towards higher wavelength in the visible range of the spectrum showing a decrease in intensity with increase in the duration of exposure of MW irradiation. For the 2‐mercaptoethanol capped CdS nanocrystals in solution, the photoluminescence peak remains nearly at the same position, showing a decrease in intensity, with increase in duration of exposure of MW irradiation. The CdS nanocrystals were also characterized by XRD and FTIR. The relative PL quantum yield of the CdS nanocrystallites was estimated under various experimental conditions. The formation of sulfur vacancies (surface defects) on CdS nanocrystallites in DMF for both the capping agents were indicated by emission measurements. The estimated relative PL quantum yield decreases systematically with increase in MW exposure for both 1‐butanethiol and 2‐mercaptoethanol capped CdS nanocrystallites.