Optically Switchable Fluorescence Enhancement at Critical Interparticle Distances

Plasmonic nanostructures provide electric field localization to be used as a fluorescence enhancement tool for the closely located fluorophores. However, metallic structures exhibit nonradiative energy transfer at close proximity, which suppresses the boost in the photoluminescence spectrum due to the inhomogeneous medium. Compensation to nonradiative losses is fundamentally restricted, therefore, defining the critical interparticle distances, where the fluorescence enhancement is detectable, holds utmost importance for device applications. In this work, the critical interparticle distances of a metal nanoparticle (MNP) and quantum emitters (QEs) with angstrom resolution by analyzing the interplay between quantum yield and nonradiative decay are numerically identified. By engaging a collimated light application on silver nanoparticle (AgNP) placed at a critical distance, an active fluorescence enhancement switch yielding an observable sevenfold increase in fluorescence intensity is simulated. The provided free space simulation includes the complete response of AgNP with retardation and higher order multi-polar effects, for which the previous analytical works fall short. While the model bridges the absorption and emission spectra via corresponding Stokes shift values and presents a general approach for the interaction of QEs and MNPs in the Rayleigh regime, it can be extended to the Mie regime for larger QEs and can be modified for a dielectric device environment.