Molecular hot electroluminescence due to strongly enhanced spontaneous emission rates in a plasmonic nanocavity
Molecular hot electroluminescence due to strongly enhanced spontaneous emission rates in a plasmonic nanocavity
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由于等离激元纳米腔中自发发射率的强烈增强而产生的分子热电致发光
DOI：
10.1039/c4nr06519k
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发表时间：
2015-01-01
期刊：
影响因子：
6.7
通讯作者：
Dong, Zhen-Chao
中科院分区：
文献类型：
--
作者：
Chen, Gong;Li, Xiao-Guang;Dong, Zhen-Chao
我们最近已经证明了来自扫描隧道显微镜的隧道结中的分子的异常无弛豫热电致发光[Dong等人，Nat.Photonics，2010，4，50]。在本文中，基于物理现实的参数，我们的目标是解开潜在的物理机制，使用多尺度建模方法，结合经典的广义Mie理论与量子主方程。我们发现，纳米腔等离子体激元调谐的自发辐射率在塑造光谱轮廓中起着至关重要的作用。特别是，在共振时，辐射衰变率可以提高三到五个数量级，这使得辐射过程能够在皮秒的寿命尺度上发生，并与振动弛豫竞争。如此大的珀塞尔效应开辟了新的发射通道，以产生直接由分子激发态的更高电子振动能级产生的热发光。我们还强调，共振等离子体纳米腔在隧穿电子诱导的分子发光的关键作用是通过等离子体增强的真空波动，而不是产生一个有效的等离子体激元受激发射过程，以提高自发辐射衰减。这种改进的理解在以前的研究中被部分忽视，但被认为是非常重要的分子等离子体和光电子学的进一步发展。
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.