Optically Switchable Fluorescence Enhancement at Critical Interparticle Distances

Abstract

Plasmonic nanostructures provide electric field localization to be used as a fluorescence enhancement tool for the closely located fluorophores. However, metallic structures exhibit non-radiative energy transfer at close proximity, which suppresses the boost in the photoluminescence spectrum due to inhomogeneous medium. Compensation to non-radiative losses is fundamentally restricted, therefore defining the critical interparticle distances, where the fluorescence enhancement is detectable hold utmost importance for device applications. In this work, we numerically identified the critical interparticle distances of a metal nanoparticle (MNP) and quantum emitters (QEs) with angstrom resolution by analyzing the interplay between quantum yield and non-radiative decay. By engaging a collimated light application on silver nanoparticle (AgNP) placed at a critical distance, we simulated an active fluorescence enhancement switch yielding observable 7-fold increase in fluorescence intensity. 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 Rayleigh regime, it can be extended to Mie regime for larger QEs and can be modified for dielectric device environment.