Charge state and energy transfer investigation of iron-chromium co-doped ZnS polycrystalline prepared by step-temperature diffusion for mid-infrared laser applications

The spectroscopic characterization and energy transfer mechanism of iron-chromium co-doped ZnS polycrystalline (Cr,Fe:ZnS) were reported with dimension of 10 mm × 10 mm × 1.5 mm produced by step-temperature thermal diffusion method. The infrared absorption is characterized by two absorption broad-bands centered at 1.67 μm and 2.9 μm which can be attributed to the spin-allowed transition 5T2↔5E within the 3 d4 shell of Cr2+ and Fe2+ ions. The valences of iron and chromium in ZnS were analyzed by X-ray photoelectron spectroscopy. Photoluminescence spectrum shows a relatively strong broad emission band centered at 4 μm with a width of 800 nm (FWHM) under 1.56 μm excitation at room temperature and reveals an effective Cr2+→Fe2+ energy transfer process. The measured photoluminescence decay was about 5 μs at room temperature. All the results indicate that Cr,Fe:ZnS could be used as the gain medium operating at 3.5–4.5 μm via Cr2+→Fe2+ energy transfer using a more convenient laser pump source in the near IR region.