Is there a proper figure of merit for a plasmonic structure involved in metal-enhanced fluorescence?

TL;DR

This paper proposes a new, unambiguous figure of merit for evaluating plasmonic structures in metal-enhanced fluorescence, based on the maximal fluorescence enhancement factor at quantum yield one.

Contribution

It introduces a standardized figure of merit, $ ext{F}_{q_0=1}$, that removes dependence on emitter quantum yield, improving assessment of plasmonic structures for MEF.

Findings

$ ext{F}_{q_0=1}$ is a consistent measure for MEF performance.

Other enhancement factors can be derived from $ ext{F}_{q_0=1}$ by simple scaling.

The proposed metric clarifies the evaluation of plasmonic nanostructures in fluorescence enhancement.

Abstract

A suitability of a nanostructure for a metal-enhanced fluorescence (MEF) is usually assessed from the value of the maximal fluorescence enhancement factor, $\mathcal{F}$, which it can generate. However, $\mathcal{F}$ is an ambiguous quantity which may dramatically depend on the intrinsic quantum yield, $q_0$, of the emitter in a free space. Here we suggest $\mathcal{F}=\mathcal{F}_{q_0=1}$ taken in the limiting case of $q_0=1$ as a proper figure of merit for a plasmonic structure involved in MEF. Any other realistic $\mathcal{F}$ in the MEF regime can be recovered from $\mathcal{F}_{q_0=1}$ by a simple $1/q_0$ scaling.