Resonant defect recombination-localized surface plasmon energy transfer and exciton dominated fluorescence in ZnO-Au-ZnO multi-interfaced heteronanocrystals

The semiconductor-metal heteronanocrystals (HNCs) that possess a perfect epitaxial interface can accommodate novel and interesting physical phenomena owing to the strong interaction and coupling between the semiconductor excitons and metal plasmons at the interface. Here, we fabricate the pyramidal ZnO-Au HNCs and study their unique photophysical properties. Several Au nanospheres are perfectly epitaxially bound with a single ZnO nanocrystal owing to the small lattice mismatch between them and there are also ZnO-Au-ZnO sandwiched HNCs. There is strong coupling between the green defect-associated recombination in the ZnO nanocrystal and the localized surface plasmon resonance (LSPR) of the Au nanoshpere at the interface of the HNC. This leads to resonant defect recombination-LSPR energy transfer and resultant nearly complete quenching of the green defect luminescence of the ZnO NCs in the HNCs, leaving only the UV exciton luminescence. The lifetimes of both the green and UV emission bands decrease significantly in the ZnO-Au HNCs relative to that of the pure ZnO nanocrystals owing to the combined effect of resonance energy transfer and surface plasmon enhanced radiative transition. The exponent of the luminescence intensity-excitation intensity power function for the green emission band is remarkably smaller than unity and this suggests that the involved defects have an intermediate concentration.