Optical properties of annealed Mn2+-doped ZnS nanoparticles
Cysteine stabilized ZnS and Mn2+-doped ZnS nanoparticles were synthesized by a wet chemical route. Using the ZnS:Mn2+ nanoparticles as seeds, silica-coated ZnS (ZnS@Si) and ZnS:Mn2+ (ZnS:Mn2+@Si) nanocomposites were formed in water by hydrolysis and condensation of tetramethoxyorthosilicate (TMOS). The influence of annealing in air, formier gas, and argon at 200–1000 °C on the chemical stability of ZnS@Si and ZnS:Mn2+@Si nanoparticles with and without silica shell was examined. Silica-coated nanoparticles showed an improved thermal stability over uncoated particles, which underwent a thermal combustion at 400 °C. The emission of the ZnS@Si and ZnS:Mn2+@Si passed through a minimum in photoluminescence intensity when annealed at 600 °C. Upon annealing at higher temperatures, ZnS@Si conserved the typical emission centered at 450 nm (blue). ZnS:Mn2+@Si yielded different high intensity emissions when heated to 800 °C depending on the gas employed. Emissions due to the Mn2+ at 530 nm (green; Zn2SiO4:Mn2+), 580 nm (orange; ZnS:Mn2+@Si), and 630 nm (red; ZnS:Mn2+@Si) were obtained. Therefore, with a single starting product a set of different colors was produced by adjusting the atmosphere wherein the powder is heated.