Microwave synthesis of manganese-ion-doped zinc sulfide nano-phosphors using a novel monomer

ZnS:Mn2+ nano-phosphors are synthesized via a microwave irradiation technique using zinc 2-ethylhexanoate as a novel zinc precursor. The developed process produces ZnS:Mn2+ nano-particles having in situ capping of 2-ethylhexanoic acid on the surface, resulting in high luminescence intensity due to effective surface passivation. Surface characterization of the nano-particles indicates that 2-ethylhexanoic acid is chemisorbed as carboxylate onto the surface of ZnS:Mn2+ nano-particles and the two oxygen atoms in the carboxylate are coordinated symmetrically to the Zn atoms, leading to the formation of the covalent Zn–O bond. The anion bound onto the nano-particle surface prevents particle agglomeration due to electrostatic repulsion between two adjacent particles. Electron spin resonance (ESR) spectrum showed a hyperfine sextet revealing the fact that Mn2+ in ZnS was present as dispersed Mn2+ impurities rather than Mn2+ clusters, which would produce broad resonance without splitting. The samples showed bright yellow-orange luminescence at about 585 nm, characteristic of 4T1 (excited) → 6A1 (ground) transition of Mn2+ ion at Td symmetry in ZnS.