Structural, photoconductivity and photoluminescence characterization of cadmium sulfide quantum dots prepared by a co-precipitation method

• Published in: Electronic materials letters Vol. 7; no. 1; pp. 31 - 38
• Main Authors: Mishra, Sheo K., Srivastava, Rajneesh K., Prakash, S. G., Yadav, Raghvendra S., Panday, A. C.
• Format: Journal Article
• Language: English
• Published: Springer The Korean Institute of Metals and Materials 01.03.2011; 대한금속·재료학회
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed Matter Physics; Materials Science; Nanotechnology; Nanotechnology and Microengineering; Optical and Electronic Materials; 전자/정보통신공학; quantum dots; negative photoconductivity; CdS; photoluminescence
• ISSN: 1738-8090; 2093-6788
• DOI: 10.1007/s13391-011-0305-6

In this paper, cadmium sulfide (CdS) quantum dots (QDs) are synthesized by a simple co-precipitation method. X-ray diffraction (XRD) confirmed the formation of a cubical zinc blend structure of CdS nanoparticles. Transmission Electron Microscopy (TEM) images revealed that the CdS QDs are of 2–5 nm in size. The UV-vis absorption spectra showed an absorption peak at 427 nm (∼2.90 eV) indicating a blue shift of 0.48 eV as compared to bulk CdS. We estimated the particle sizes with the help of X-ray diffraction (XRD) patterns (3.665 nm) and the shift of the band gap absorption in the UV-vis spectrum (4.276 nm), which is very close to the TEM micrograph result. The photoluminescence spectrum shows three major emission peaks centered at 453 nm (∼2.73 eV), 526 nm (∼2.35 eV) and 551 nm (∼2.24 eV) at room temperature, which may be attributed to excitonic transitions, donor-acceptor (D-A) pairs recombination and the sulphur interstitial defects (Is) present in the band gap. To study the photoconductivity, the field dependence of the photocurrent and the dark-current was assessed, as was the time-resolved rise and decay photocurrent spectrum and wavelength-dependence photocurrent spectrum assessment of the CdS QDs. The time-resolved rise and decay photocurrent spectra exhibited negative photoconductivity (NPC) behavior when the CdS QDs were illuminated with 490 nm light. Such anomalous NPC may be attributed to the light-induced desorption of water molecules. The wavelength-dependence of the photocurrent was found to be close to the absorption and PL spectrum. The photoconductivity properties of the CdS QDs were measured using a thick film of powder without any binder. These CdS QDs can find potential application in optoelectronic devices and photodetectors.