Hot-pressed Cr2+-doped ZnS transparent ceramics from combustion-synthesized nanoparticles: Processing and luminescence properties

Transparent Cr 2+ -doped ZnS ceramics with a nominal Cr concentration ranging from 50 to 3000 ppm were fabricated by hot pressing. ZnS nanopowders with controlled Cr content were synthesized by a combustion method and treated in H 2 S/N 2 to remove oxide impurities. X-ray diffraction showed that both powders and ceramics were predominantly cubic ZnS with minor hexagonal ZnS; impurity phases (ZnO, Zn 3 O(SO 4 ) 2 ) present after combustion were eliminated. Powders consisted of ∼100 nm primary particles, and doping had little effect on morphology. Ceramics achieved >99.5% theoretical density with ∼0.7 μm grain size, regardless of Cr content. Undoped ceramics exhibited mid-infrared transmission near the theoretical limit (∼75%); increasing Cr content reduced transmission (though still being high up to 1000 ppm) and introduced visible absorption attributed to Cr 3+ in a ZnCr 2 S 4 spinel phase. Optical spectra revealed broad Cr 2+ ( T d ) related absorption (1.3-2.1 μm, peaking at ∼1.7 μm) and broad luminescence (1.6-3.0 μm, peak at ∼1.91 μm). A luminescence lifetime of ∼6 μs was measured for all samples indicating that concentration quenching effects are limited in the investigated range. These results demonstrate that Cr 2+ :ZnS ceramics have promising mid-IR emission properties suitable for 2–3 μm solid-state lasers.