Synthesis of copper ion doped ZnS phosphor sols by peptization process of sulfide-citrate complex precipitates

Optically transparent and stable sols of copper ion doped zinc sulfide (ZnS:Cu) nanoparticles were obtained by heating a mixture of ethylene glycol aqueous solution and sulfide precipitate at 348 K for 24 h. The sulfide precipitates containing zinc ions, copper ions and citrate ions were peptized in an aqueous solution of ethylene glycol having a 0.5 molar fraction of [Ethylene glycol]/([H2O]+[Ethylene glycol]). Photoluminescence characteristics and stability of the sols depended on the amount of citrate ions in the aqueous solution which was used for preparing sulfide precipitates. The citrate ions strongly affected the characteristics of the obtained sols with dispersion of the copper ion doped-ZnS nanoparticles. According to TG–DTA curves and N2 adsorption isotherms of the precipitated sulfides, the citrate ions in the aqueous solution containing zinc ions, copper ions coprecipitated in the sulfide precipitates formed by adding the sodium sulfide aq. The citrate ions played an important role for the peptization and the formation of stable sols.