Large-scale hydrothermal synthesis and optical properties of Cr2+:ZnS nanocrystals

Cr2+:ZnS is an important mid-infrared laser material, and Cr2+:ZnS nanopowders are very important for the fabrication of transparent ceramics. In this paper, Cr-2 :ZnS nanopowders were synthesized via a hydrothermal method, in which thioacetamide (TAA) was adopted as sulfur source and reducing agent to avoid the oxidation of Cr2+ ions. The influences of the hydrothermal time and [Zn2+]/[TAA] ratio on the morphology and particle size of the nanopowders were investigated systematically as well as the reaction mechanism. It is believed that the orientated attachment and Oswald ripening both occurred during the hydrothermal reaction, which resulted in the formation of bimodal particle size distribution. After calcination of the nanopowders under Ar/H-2 atmosphere, the Cr-2+ ions were successfully doped into the Zn2+ lattice sites, which was supported by the X-ray powder diffraction patterns, the absorption and photoluminescence spectra of the calcination products. The optical properties were similar with those of the samples obtained by thermal diffusion, which means that they have the potential application in the fabrication of Cr2+:ZnS transparent ceramics.