Synthesis and fluorescence properties of pure and metal-doped spherical ZnS particles from EDTA-metal complexes

Monodispersed spherical ZnS particles as well as doped with Cu, Mn ions were synthesized from metal-chelate solutions of ethylenediamine tetraacetate (EDTA) and thioacetamide (TAA). The characterizations of the ZnS-based particles were investigated via TEM, SEM, XRD, TG/DTA and PL measurements. The sphere size was controlled from 50 nm to 1 μm by adjusting the nucleation temperatures and molar ratio of Zn-EDTA to TAA. The emission intensity continuously increased with the increase of the particle size. When the ZnS microspheres were annealed at 550-800 °C, there were two specific emission bands with the centers at 454 nm and 510 nm, which were associated with the trapped luminescence arising from the surface states and the stoichiometric vacancies, respectively. When Cu²⁺ was introduced into ZnS microspheres, the dominant emission was red-shifted from 454 to 508 nm, fluorescence intensity also sharply increased. However, for the Mn²⁺-doped ZnS, the emission intensity was significantly enhanced without the shift of emission site.