Synthesis of a stable sol of Mn2+-doped ZnS nanoparticles by low-temperature heating of sulfide precipitate in ethylene glycol

Abstract

A sol of Mn2+-doped ZnS nanoparticles was prepared by heating a ZnS precipitate with Mn2+ ions in ethylene glycol at 348 K for 24 h. The precipitate was prepared by mixing the aqueous solution of Zn(NO3)2·6H2O and Mn(NO3)2·6H2O with an aqueous solution of Na2S According to the UV–VIS absorption spectra, when the wavelength was more than 400 nm, the optical absorptions of the obtained sols with the molar fraction of Mn2+ ions in the solution (XSolution: the molar fraction of Mn2+/(Mn2+ + Zn2+) in the aqueous solution) less than 0.02 were less than 0.12 and the obtained sols were clear and transparent for the visible light. The sol of Mn2+-doped ZnS nanoparticles showed PL characteristics when irradiated with an excitation light with a wavelength of 345 nm. Accordingly, a simple process to heat the mixture of the sulfide precipitate and ethylene glycol at 348 K enabled us to obtain a homogeneous transparent sol of Mn2+-doped ZnS nanoparticles with PL characteristics. According to the results of the chemical analysis of the molar fraction of Mn2+ in the obtained precipitate (XPrecipitate) and the nanoparticles in the sols (XNano), the XNano was less than that the XPrecipitate as compared with the same XSolution. The Mn2+ ions in the nanoparticles were dissolved in the solvent during the heat treatment since the solubility product of MnS was much larger than that of ZnS. As such, the dissolution-precipitate process played an important role in the formation of the sol.