Optical and electronic correlation in Mg-doped nano cadmium sulfide

Nano Cd_0.9Mg_0.05S was synthesized applying the thermolysis technique in air and under flow of nitrogen. Samples obtained exhibited CdS structure with two phases. Rietveld refinement analysis was used to determine the different structure parameters. Analysis of UV–Vis absorption spectra disclosed that the optical band gap of CdS sample prepared in N₂ is less than that of the corresponding sample prepared in air. The optical band gap of CdS (air) sample was decreased as it doped with Mg while it increased as Mg doped CdS (N₂) sample. The photoluminescence (PL) intensities of CdS samples were enhanced when they doped with Mg. Moreover, the PL intensity of CdS (air) increased further as it prepared under nitrogen. The emitted PL colors (violet, blue and green) depended on the condition of preparation of the different samples. Density functional theory calculation (DFT) was applied to explain the variation in the optical band gap of CdS upon doping with Mg. DFT calculation revealed that the absorption, refractive index, extinction coefficient, the dielectric properties and photoconductivity response were affected by the kind of defects in the sample. Mg-doped stoichiometric or non-stoichiometric CdS have a non-magnetic nature.