Au-spotted zinc oxide nano-hexagonrods structure for plasmon-photoluminescence sensor

Abstract This study presents the defectless zinc oxide nano-hexagonrods (ZnO-NH) structure decorated by gold nanoparticles (AuNPs) and its enhancement due to the tunable plasmonic field for photoluminescence sensor. The ZnO-NHs were grown on ITO glass substrate via a low-cost hydrothermal method followed by annealing at different seeding temperatures, respectively. A correlation has been established between annealing temperature and the defect level concerning the diameter and density of ZnO-NH verified by Raman and FE-SEM images analysis. A further coating of the gold layer over ZnO-NH via thermal evaporator exhibits the plasmonic field enhancement in visible range which revives after short rapid annealing treatment. The enhancement is due to the large surface area of the sensing area on the haxagonrods shape and robust plasmonic coupling between metal and ZnO which efficiently detects fluorescence signal of Rhodamine 6G(R6G)  molecules. A drastic change of tunable enhanced signal was resulted by AuNPs size and morphology and elucidated by suitable energy diagram observed from quenching to highly enhanced signal using photoluminescence spectrum and its related linearity plot. Carried out in three different thicknesses of AuNPs spotting on ZnO-NH, 3, 5 and 7 nm, it was observed that 3 nm AuNPs resulted in six times higher enhancement of output signal at seeding temperature of 500 o than the 5 and 7 nm gold NPs spotted ZnO-NH at same experimental conditions. By the proposed structure, a significant photoluminescence and plasmonics enhancement, the ease of tunability, and higher uniformity were achieved by the localized surface plasmon resonance (LSPR) from the AuNPs-decorated ZnO-NH and annealing process. Overall, the AuNPs- ZnO-NH hybrid offers a low-cost and simple fabrication potentially applied in a high-sensitive smart surface plasmonic optical sensor applications and can be a representative of new generations of photodiodes, solar cells, and metamaterials.