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

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.