The Influence of CdS on the Structural and Optical Properties of Nano ZnWO₄

Abstract

We investigated the influence of CdS on the structural and optical properties of nano ZnWO 4 for optical applications. (1−x)ZnWO 4 /xCdS (x; 0 to 0.25) heterojunctions were formed and the structure and microstructure of the ZnWO 4 and CdS phases developed were investigated using Rietveld refinement analysis for synchrotron X-ray diffraction data. Phase analysis revealed the phase percentage of the CdS phase is always less than the nominated value (x), implying merging of some Cd and S into ZnWO4. Raman spectra showed CdS peaks, confirming the existence of CdS. Scanning electron microscopy showed two distinct morphologies: plate-like particles (ZnWO 4 phase) and spherical shape (CdS phase). UV–vis diffuse measurements revealed enhancement of absorbance and reduction in reflectance and transmittance, in the range 300–56 nm, as the amount of CdS (x) increased in the (1−x)ZnWO 4 /xCdS system. Band gap of the ZnWO 4 phase reduced from 4.0 eV for x = 0.0 to 3.9, 3.6, and 2.9 eV for x = 0.05, 0.1, and 0.25, respectively. The highest refractive index values were obtained as the amount of CdS reached 0.05. Impact of alloying on linear and nonlinear parameters and emitted photoluminescence spectra was studied. Upon loading ZnWO 4 with CdS, the PL intensity is greatly quenched and the whole spectrum is red shifted, from 480 to 540 nm. CIE chromaticity diagrams show that ZnWO 4 sample without any doping exhibits a blue color while the doped system reveals green-yellow colors.