Chen Gong, Li Xiao-Guang, Zhang Zhen-Yu, Dong Zhen-Chao
International Center for Quantum Design of Functional Materials, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
Nanoscale. 2015 Feb 14;7(6):2442-9. doi: 10.1039/c4nr06519k.
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.
我们最近在扫描隧道显微镜的隧道结中展示了分子的反常无弛豫热致发光现象[董等人，《自然·光子学》，2010年，第4卷，第50页]。在本文中，基于实际的物理参数，我们旨在使用一种将经典广义米氏理论与量子主方程相结合的多尺度建模方法来揭示其潜在的物理机制。我们发现，纳米腔等离子体调谐的自发发射率在塑造光谱轮廓方面起着关键作用。特别是在共振时，辐射衰减率可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，以产生直接源于分子激发态较高振动态的热发光。我们还强调，共振等离子体纳米腔在隧穿电子诱导分子发光中的关键作用是通过等离子体增强的真空涨落来增强自发辐射衰减，而不是产生有效的等离子体受激发射过程。这种更深入的理解在以前的研究中部分被忽视了，但被认为对分子等离子体学和光电子学的进一步发展非常重要。
