Studies of mechanisms and characteristics of the fluorescence enhancement on anodic aluminum oxide thin film

Anodic aluminum oxide (AAO) thin film recently has been found as a new type of fluorescence enhancement nanomaterial. However, the mechanisms of the AAO thin film for the fluorescence enhancement have not been completely understood. Herein, the studies of its mechanisms are reported. Based on the experimental and modeling results, it has been found that the main contributing factor to the fluorescence enhancement is probably the plasmonic Al nanoparticles (NPs) embedded in the film, while the nanopore size and porosity of AAO thin film have a limited contribution. The characteristics of the enhancement have also been studied. It has been found that the enhancement is highly related to the gap between the fluorophore and the surface of the AAO thin film. Different excitation wavelength also results in different fluorescence enhancement. Using a simple model with a layer of Al NPs uniformly distributed in the thin film, the calculated enhancement factor of electric field and characteristics of the fluorescence enhancement match the experimental results.