Selective tuning of enhancement in near band edge emission in hydrothermally grown ZnO nanorods coated with gold

The room-temperature photoluminescence (PL) spectra of hydrothermally grown ZnO nanorods (NRs) coated with Au using dc sputtering and thermal evaporation were systematically investigated. Au coated (via dc sputtering) ZnO NRs were found to exhibit very large near band edge emission enhancement, on the contrary Au coated (via thermal evaporation) ZnO NRs showed suppression in the near band edge emission peak. These observed results were further confirmed by excitation intensity (EI) dependent PL spectra of different samples. Further using Raman spectra it has been observed that the longitudinal optical (LO) phonons exhibit an enhancement and a weakening by the Au coatings, using dc sputtering and thermal evaporation respectively. Finally by controlling the concentration of KMnO4 as an additive during the hydrothermal growth, selective tuning in the defect density was carried out, which was later utilized to probe the effect of defect density of the Au-ZnO plasmonic coupling. Moreover, our results strongly suggest that the EI dependent PL has a strong dependence on the metal coating technique. The findings presented in this article clearly indicate the dependence of Au-ZnO plasmonic coupling on the overall defect density and the process of Au deposition.