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Issue 6, 2015
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Molecular hot electroluminescence due to strongly enhanced spontaneous emission rates in a plasmonic nanocavity

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Abstract

We have recently demonstrated anomalous relaxationless hot electroluminescence from molecules in the tunnel junction of a scanning tunneling microscope [Dong et al., Nat. Photonics, 2010, 4, 50]. In the present paper, based on physically realistic parameters, we aim to unravel the underlying physical mechanism using a multiscale modeling approach that combines classical generalized Mie theory with the quantum master equation. We find that the nanocavity-plasmon-tuned spontaneous emission rate plays a crucial role in shaping the spectral profile. In particular, on resonance, the radiative decay rate can be enhanced by three-to-five orders of magnitude, which enables the radiative process to occur on the lifetime scale of picoseconds and become competitive to the vibrational relaxation. Such a large Purcell effect opens up new emission channels to generate the hot luminescence that arises directly from higher vibronic levels of the molecular excited state. We also stress that the critical role of resonant plasmonic nanocavities in tunneling electron induced molecular luminescence is to enhance the spontaneous radiative decay through plasmon enhanced vacuum fluctuations rather than to generate an efficient plasmon stimulated emission process. This improved understanding has been partly overlooked in previous studies but is believed to be very important for further developments of molecular plasmonics and optoelectronics.

Graphical abstract: Molecular hot electroluminescence due to strongly enhanced spontaneous emission rates in a plasmonic nanocavity

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Article information


Submitted
05 Nov 2014
Accepted
19 Dec 2014
First published
22 Dec 2014

Nanoscale, 2015,7, 2442-2449
Article type
Paper
Author version available

Molecular hot electroluminescence due to strongly enhanced spontaneous emission rates in a plasmonic nanocavity

G. Chen, X. Li, Z. Zhang and Z. Dong, Nanoscale, 2015, 7, 2442
DOI: 10.1039/C4NR06519K

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