Surface-plasmon mediated photoluminescence from Ag-coated ZnO/MgO core–shell nanowires

• ZnO–MgO core–shell nanowire structure exhibits optical cavity effects.
• Optical cavity effects result in greatly enhanced band-edge emission.
• Ag nanoparticles exhibit plasmon–exciton coupling.
• Coupling enhances band-edge emission while not enhancing visible emission.

Plasmon–exciton coupling mechanisms were studied in ZnO/MgO core–shell nanowires by comparing nanowires with and without a silver-nanoparticle coating. By varying the thickness of the MgO layer, it was possible to examine the distance-dependent plasmonic effects and elucidate the mechanisms responsible for enhancing the band-edge photoluminescence. The core–shell nanowires exhibited optical cavity effects as a function of MgO thickness that dramatically enhanced the band-edge photoluminescence yields in the ultraviolet. Decorating the core–shell nanowires with Ag nanoparticles resulted in a two-fold plasmonic enhancement of the band-edge emission compared to the resonant cavity effects alone. In this case, an additional differential enhancement of the band-edge emission is observed for the first higher-order mode compared to the lowest-order mode. The visible luminescence is not significantly enhanced and does not follow the trend of enhanced photoluminescence observed for the band-edge decay.