Luminescence enhancement and quenching in ZnS:Mn by Au nanoparticles

Au/silica/ZnS:Mn core-shell nanostructures were synthesized and their luminescence behaviors were investigated in comparison with that of silica-coated ZnS:Mn nanoparticles. The extinction peak of Au nanoparticles is at 520 nm which is from the surface plasmon. After silica coating, the surface plasmon extinction peak is red-shifted to 535 nm. Transmission electron microscopy observations show that some ZnS:Mn nanoparticles are adhered on the Au/silica surfaces. ZnS:Mn nanoparticles have two emissions. The emission at 442 nm is from surface defects or donor-acceptor (D-A) pairs and the emission at 600 nm is from the ⁴T₁-⁶A₁ transition of Mn²⁺. For the first time, we observed that the Mn ²⁺ emission at 600 nm was quenched but the D-A emission at 442 nm was enhanced by Au nanoparticles. This phenomenon can be explained reasonably by the radiation plasmon model that surface plasmon resonance scattering may enhance the emission while surface plasmon resonance absorption quenches the emission.