Surface Plasmon Resonance (SPR) Electron and Energy Transfer in Noble Metal−Zinc Oxide Composite Nanocrystals

Au- and Ag-ZnO composite nanocrystals having a dumbbell-like structure were successfully synthesized through the nucleation and decomposition of zinc hydroxide at the surface of pre-existing Au and Ag nanoparticles, respectively. The average size of the Au and Ag nanoparticles used was ∼4 nm and that of the ZnO nanocrystals was ∼10 nm. The composite nanocrystals show strong crystallinity of face-centered cubic and wurztite structures from Au or Ag and ZnO, respectively. The composite nanocrystals show enhanced UV light emission due not only to the surface electron transfer from the Au or Ag to the ZnO by the surface plasmon resonance (SPR) but also to the extension of the Fermi energy level to the ZnO. The Au-ZnO composite nanocrystals showed significantly suppressed visible light luminescence, while the Ag-ZnO did not show any apparent difference compared to the ZnO nanocrystals.