Understanding of electronic and optical properties of ZnS with high concentration of point defects induced by hot pressing process: The first-principles calculations

ZnS is one of the important optical materials for thermal imaging, infrared detecting and laser transmission. Herein, the point defects formation mechanism of hot-pressing ZnS and their influence on optical properties were systematically explored by density functional theory (DFT) to fully understand the experimental observation what the transmittance decreases and the black fogs form with the S vacancies increasing for the hot-pressing ZnS ceramics. Zn (V_Zn) and S (V_S) point vacancies with various amounts of defect concentrations in the range from 0 to 50% were systematically studied to corresponding the experimental results. The result indicates that anion V_S are energetically more favorable in regards to cation V_Zn based on their formation energies. This result explains why only V_S were observed in the experiment. Electronic structures show that the band gaps vary from 3.858 eV to 1.569 eV, corresponding to the V_S concentration from 0 to 25%. Consequently, the V_S also lead to the reflectivity increase and the decrease of the optical transmittance. Continuation of increasing the V_S concentrations to 50%, ZnS turns into metallic behavior without a distinctive band gap, so the light fails to pass and maybe cause black fogs formation.