Baghramyan Henrikh M, Ciracì Cristian
Center for Biomolecular Nanotechnologies, Istituto Italiano di Tecnologia, Via Barsanti 14, 73010 Arnesano, LE, Italy.
Nanophotonics. 2022 Jan 25;11(11):2473-2482. doi: 10.1515/nanoph-2021-0707. eCollection 2022 Jun.
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 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.
等离子体纳米颗粒为增强荧光发射提供了理想的环境。一方面，它们能局部放大电磁场，提高发射体的激发速率；另一方面，它们提供了高局部态密度，加速自发发射。然而，当发射体紧邻单个金属纳米颗粒放置时，非辐射态的数量会急剧增加，导致荧光猝灭。从理论上预测，通过明智地放置发射体，等离子体纳米腔中的荧光可以单调增加。在本文中，我们表明这种单调增加是由于在描述金属纳米颗粒的等离子体响应时使用了局部响应近似。我们证明，通过量子流体动力学理论考虑电子隧穿和周围系统的非局域性，最终也会导致当发射体置于纳米腔中时荧光增强的猝灭，这与局部响应和托马斯 - 费米流体动力学理论的结果相反。这一结果标志着考虑量子效应，特别是电子隧穿对于正确描述纳米尺度等离子体系统中的发射效应的重要性。
