Synthesis and Characterization of Nanocrystalline CdS Thin Films in PVA Matrix

Polymer embedded Cadmium Sulphide (CdS) nanoparticles were synthesized by a chemical route using organic substance as the desired matrix. In the present work, cadmium sulphate and thiourea, dissolved in an alkaline medium, were taken as the source of cadmium and sulphur, respectively. The CdS nanoparticles are polycrystalline and are composed of ultrasmall closely packed nanocrystallites. The size and distribution of the crystallites are controlled by varying the temperatures of the bath solution from 28-80 degrees C. The crystallite sizes of the CdS films are determined from X-ray diffraction lines and it shows a preferred orientation along the (002) plane. The sizes are found to vary from 7.6 to 12.4 nm. The sizes of the crystallites are determined by SEM also. The band gap of the nanocrystalline material is determined from the UV absorption spectroscopy. The absorption edge is shifted towards the lower wave length side (i.e., blue shift) and are found to be within the range from 2.48 to 2.8 eV. The band gap increases with the increase of deposition temperatures. Photoluminescence measurements on the CdS nanoparticles show an emission spectrum with two subbands that are attributed to band-edge and surface-defect emissions. The peak position, intensity, and width of the band-edge emission band are closely related to the size of the crystallites in the CdS.