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Preparation and optical properties of transparent polycrystalline ZnS bulk materials

The transmittance of chemical vapor deposition (CVD) ZnS can be effectively improved through the processing of hot isostatic pressing (HIP) in inert gas, especially in the waveband of visible light and near infrared. In general, the size of the particles of the polycrystalline ZnS bulk material can be increased after the processing of HIP. This change can definitely affect the optical properties and mechanical properties of the material. In this paper, a two-step method was applied to improve preparation of transparent polycrystalline ZnS bulk materials. The first step was the growth of polycrystalline ZnS through dynamic CVD. Then the grown polycrystalline ZnS bulk materials was annealed in inert gas at 800~900°C for 10～50 h. Experimental results showed that the optical properties and mechanical properties of the materials have been significantly improved. The average transmission rate of the materials was over 74% in the wavebands 8~12 μm and was over 70% in the mid-infrared 3~5 μm. The absorption peak of the materials at 6 μm attributed to Zn-H complex and S vacancy was obviously decreased. Furthermore, results of imaging experiments showed that lenses made of the annealed transparent polycrystalline ZnS bulk materials has excellent performance in optical properties and modulation transfer function (MTF).