Effect of Zn/S non-stoichiometric ratio on the structural, optical and electronic properties of nano-ZnS

Abstract

Non-stoichiometric ZnS nanomaterials were prepared using a thermolysis procedure by decreasing the stoichiometric amount of thiourea relative to the amount of zinc acetate as starting precursors: Zn(Ac)/(1−x) thiourea (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5). The high-resolution transmission electron microscope revealed the nanonature of the obtained samples. The X-ray diffraction analysis applying Rietveld method was carried out to explore the influence of Zn/S non-stoichiometry on the structural and microstructural properties of the crystalline phases in the samples. ZnO phase appeared for x ≥ 0.2 forming ZnS1–x/ZnO heterostructures; its percentage increased with increasing non-stoichiometric parameter (x).Incorporation of oxygen ions into the ZnS lattice compensating the sulfur deficiency was manifested by Fourier transform infrared spectroscopy. The UV–Vis analysis revealed the decrease in the bandgap of ZnS from 3.42 eV for x = 0.0 to 2.71 eV for x = 0.5, making these materials suitable for new applications. The influence of non-stoichiometric parameter (x) on the photoluminescence emissions of formed samples was examined; results indicated the spectrum shift towards higher wavelengths. Density function calculations were performed in order to compare the electronic and optical properties of sulfur-deficient ZnS0.9 (single phase) with the ZnS sample.