Chalcogenide Letters Vol. 6, No. 8, September 2009, p. 421 – 426 SYNTHESIS AND STRUCTURAL PROPERTIES OF WURTZITE TYPE CdS NANOPARTICLES VINEET SINGH * , PRATIMA CHAUHAN Deptt of Physics, University of Allahabd, Allahabd, India, 211002 CdS semiconductor nanoparticles were synthesized by chemical precipitation method using cadmium chloride as cadmium source and sodium sulphide as sulphur source. Structural characterization of as synthesized semiconductor nanoparticles were performed by X-ray diffraction pattern (XRD) and Raman spectroscopy while optical characterization were done by Photoluminescence spectroscopy and UV-Visible absorption spectroscopy. XRD pattern showed the as synthesized CdS nanoparticles have wurtzite structure with 6- 10 nm average crystallite size. Raman spectrum also confirmed the as synthesized sample was of CdS nanoparticles having first Longitudnal optical phonon (1LO) mode at 299 cm -1 and 2LO at 601 cm -1 . UV-Visible absorption spectrum showed the blue shift in absorption edge w.r.t. bulk CdS. Photoluminescence study was performed to investigate the several defects and vacancy levels in the synthesized CdS nanopaerticles. (Received May 13, 2009; accepted September 12, 2009) Keywords: CdS, Wurtzite, Nanoparticle, Synthesis, XRD, UV-Vis, Semiconductor 1. Introduction Nanoparticles have attracted great interest in recent years because of their unique chemical, physical, optical, electrical and transport properties which are different from those of either the bulk materials or single atoms[1,2]. Due to the vast surface area, all nanostructured materials posses a huge surface energy and thus, are thermodynamically unstable or metastable. One of the great challenges in fabrication and processing of nanomaterials is to overcome the surface energy and to prevent the nanomaterials from growth in size driven by the reduction of overall surface energy. Due to high surface energy of the nanoparticles, they are extremely reactive and most systems without protection or passivation of their surfaces undergo aggregation[3]. Organic stabilizers are usually used to prevent nanoparticles from aggregation by capping their surfaces[4]. CdS is an II –VI semiconductor. Bulk CdS has hexagonal wurtzite -type structure [5], melting point 1600 0 C [6] and band gap E g =2.42 eV [7] at room temperature and pressure. As the semiconductor nanoparticles exhibit size dependent properties, the melting point of 2.5 nm CdS crystallites is as low as ~ 400 0 C [6], the band gap of 0.7 nm CdS crystallites is 3.85 eV [8] and at very high pressure phase changes from hexagonal wurtzite type to rock salt cubic phase [9].Since CdS has 2.42 eV (515 nm) band gap, so it is most promising candidate among II-VI compounds for detecting visible radiation. As CdS has wide band gap, it is used as window material for hetero junction solar cells to avoid the recombination of photogenerated carriers which improves the solar cells efficiency [10]. It has also application in light emitting diodes [11], photo detectors [12], Sensors [13], address decoders [14], and electrically driven lasers [15]. In this paper we report a simple chemical precipitation synthesis route at room temperature without using any capping agent. CdS nanoparticles were synthesized by several other methods given as controlled precipitation reaction method, rapid hot-injection based synthesis method, photochemical method and physical methods etc.