Study On The Preparation And Tunable Near/Mid-infrared Luminescence Properties Of Cr-doped ZnS

In recent years,near/mid-infrared（1³ μm） fluorescence and lasers have attracted much attention due to their important applications in many fields, such as communications, medical, laser radar, remote sensing technology and environmental monitoring. Rare earth ions（e.g., Yb3+, Nd3+, Tm3+, Ho3+, Er3+, Dy3+, Pr3+） and transition metal ions(e.g., Cr²⁺, Co²⁺, Ni²⁺) can emit near/mid-infrared. Among these ions, Cr²⁺ shows ultra-broad emission, high quantum efficiency and excellent fluorescence properties at room temperature. The fluorescence efficiency of Cr²⁺ ions is limited in glass owning to the ligand field distortion. Previous studies showed that, Cr²⁺ exhibits excellent near/mid-infrared emission properties in the zinc sulfide（ZnS） crystal. As we know, ZnS crystal is difficult to prepare a high-quality fiber optic waveguide structure. Embed Cr²⁺ doped ZnS nanocrystals into glass matrix to prepare nanocrystalline/glass composite material, then use conventional fiber drawing method to acquire the near/mid-infrared nanocrystal/glass composite active optical fiber. Therefore, it is a important task to prepare ZnS:Cr nanocrystals with excellent optical properties, regular particle morphology, uniform particle size and good dispersion.This dissertation focuses on the study of ZnS:Cr crystal preparation techniques and performance optimization method. To explore the relationship between prepare and properties of ZnS:Cr nanocrystals, the main contents include:1. Through direct precipitation-solvothermal two-step process to obtain a quasi-spherical cubic Zn S:Cr nanocrystals with 8 nm crystal size. In order to enhance the ZnS:Cr nanocrystals luminescent properties, using a reasonable dehydroxylation thermal treatment to make the pure cubic phase transform to cubic and hexagonal phase coexistence. Cr²⁺:5Eâ†'5T2 transition luminescent（1600²800 nm） in ZnS:Cr nanocrystals was obtained. However, the luminescence crystals are easy to aggregate and difficult to disperse after the dehydroxylation thermal treatment. Inorder to solve this problem, ZnS:Cr nanocluster was prepared, which has higher stability than nanocrystals. In this dissertation, single dispersion spherical ZnS:Cr nanoclusters with a particle size of ²00 nm are prepared by a homogeneous precipitation-hydrothermal two-step process. After dehydroxylation thermal treatment, Cr²⁺:5Eâ†'5T2 transition luminescent（1600²800 nm） can be realized maintaining crystalline phase, particle morphology, size and dispersion unchanged.2. In order to further broaden the Cr²⁺ luminescence emission, the near/mid-infrared emitting from ZnS:Cr and ZnS:Cr:F phosphors were prepared by a modified solid-phase method at atmospheric pressure in a short time. Compare those two phosphors, discovered that the added NaF not only plays a co-solvent and water scavenger role, but also plays a sensitizer. A broadened Cr²⁺ luminescence emission（1400²800 nm） can be detected through sensitization.