Effects of Mn²⁺ distribution controlled by carboxylic acids on photoluminescence intensity of nanosized ZnS:Mn particles

Addition of methacrylic acid (MA) during preparation of ZnS doped with Mn²⁺ (ZnS:Mn) increased the photoluminescence (PL) due to ⁴T₁-⁶A₁ transition of Mn²⁺. According to X-ray fluorescence analysis and electron paramagnetic resonance spectroscopy, ion exchange between Zn²⁺ and Mn²⁺ through a preferential dissolution of Mn²⁺ was promoted by acidic additives. This caused that Mn²⁺ ions were isolatedly incorporated into ZnS. The X-ray photoelectron spectra show that the intensity of S 2p_3/2 peak due to S⁶⁺ increased relative to that of S^2- by virtue of carboxylic groups. The intensities of PL peaks at 450 and 580 nm, corresponding to polymethacrylic acid and Mn²⁺, respectively, increased after heating at 80°C for 1 week. We conclude that MA plays important roles on selective leaching to increase the amount of isolated Mn²⁺ ions, chemical interaction between ZnS:Mn and MA, and energy transfer to Mn²⁺, leading to the increase in PL intensity.