Effect of Precursor Molar Ratio of S^2-/Zn²⁺ on Particle Size and Photoluminescence of ZnS:Mn²⁺ Nanocrystals

We investigate the influence of precursor molar ratio of S^2-/Zn²⁺ on particle size and photoluminescence (PL) of ZnS:Mn²⁺ nanocrystals. By changing the S^2-/Zn²⁺ ratio from 0.6 (Zn-rich) to 2.0 (S-rich), the particle size increases from nearly 2.7nm to about 4.0nm. The increase in the ratio of S^2-/Zn²⁺ causes a decrease of PL emission intensity of ZnS host while a distinct increase of Mn²⁺ emission. The maximum intensity for the luminescence of Mn²⁺ emission is observed at the ratio of S^2-/Zn²⁺≈1.5. The possible mechanism for the results is discussed by filling of S^2- vacancies and the increase of Mn²⁺ ions incorporated into ZnS lattices.