Luminescence enhancement of ZnO nanoparticles on metal surface

We have studied luminescence enhancement of zinc oxide (ZnO) nanoparticles with the average size of 30 nm on several metal surfaces at low temperatures. Bandedge luminescence originated from bound exciton (BE) annihilation is observed at 3.360 eV, and strongly depends on the kind and surface roughness of metal. The luminescence intensity is about 10 times larger for Ag surface than that for quartz surface. Furthermore, the luminescence increases remarkably when the roughness of Ag surface is almost the same as the particle size. The intensity ratio of the fast decay component to the slow one decreases for Ag surface compared with quartz. These results suggest that the luminescence enhancement is partially attributed to suppressing of the nonradiative recombination process in ZnO nanoparticles on metal surface.