Fluorescence quenching in plasmonic dimers due to electron tunneling

TL;DR

This paper demonstrates that quantum effects, especially electron tunneling, cause fluorescence quenching in plasmonic dimers, challenging classical predictions of continuous fluorescence enhancement at the nanoscale.

Contribution

It introduces a quantum hydrodynamic model to accurately describe fluorescence in plasmonic nanocavities, revealing quenching effects overlooked by classical theories.

Findings

Quantum tunneling leads to fluorescence quenching in nanocavities.

Classical local response models overestimate fluorescence enhancement.

Quantum effects are essential for accurate nanoscale plasmonic emission predictions.

Abstract

Plasmonic nanoparticles provide an ideal environment for the enhancement of fluorescent emission. On the one hand, they locally amplify the electromagnetic fields, increasing the emitter excitation rate, and on the other hand, they provide a high local density of states that accelerates spontaneous emission. However, when the emitter is placed in close proximity to a single metal nanoparticle, the number of nonradiative states increases dramatically, causing the fluorescence to quench. It has been predicted theoretically that, through a judicious placing of the emitter, fluorescence in plasmonic nanocavities can be increased at monotonically. In this article, we show that such monotonic increase is due to the use of local response approximation in the description of the plasmonic response of metal nanoparticles. We demonstrate that taking into account the electron tunneling and the nonlocality of the surrounding system via the quantum hydrodynamic theory results eventually in a quenching of fluorescence enhancement also when the emitter is placed in a nanocavity, as opposed to local response and Thomas-Fermi hydrodynamic theory results. This outcome marks the importance of considering the quantum effects, in particular, the electron tunneling to correctly describe the emission effects in plasmonic systems at nanoscale.