Effect of Li+ concentration on the structural and optical properties of chemically synthesized ZnS nanoparticles

ZnS nanoparticles (NPs) with different concentrations of Li-doping (0, 2.5, 4.5, 6.5, and 10.5 %) were synthesized by the co-precipitation method. Crystalline structure, surface morphologies, and optical properties were studied in detail. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) confirmed the cubic phase of un-doped and Li doped-ZnS NPs. Scanning electron microscopy (SEM) and HRTEM images showed that un-doped and Li-doped ZnS NPs contain agglomerated particles, and agglomeration is increased by increasing Li-doping. Different vibration modes are observed in a Fourier transform infrared spectrophotometer (FTIR) analysis. Defects are observed in the photoluminescence spectra (PL) of un-doped and Li-doped ZnS NPs, and a dominant green-orange transition is observed. Absorption studies using UV–vis spectroscopy reveal a quantum confinement effect for un-doped and Li- doped ZnS NPs. The direct band gap energy (Egp) increased with increasing Li concentration in the range of 3.728–3.875 eV.