Anti-Stokes Emission from Hot Carriers in Gold Nanorods
Anti-Stokes Emission from Hot Carriers in Gold Nanorods
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DOI：
10.1021/acs.nanolett.8b04359
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发表时间：
2019-02-01
期刊：
影响因子：
10.8
通讯作者：
Link, Stephan
中科院分区：
文献类型：
--
作者：
Cai, Yi-Yu;Sung, Eric;Link, Stephan
等离子体纳米粒子的光发射起源最近引起了激烈的争论。它作为表面增强拉曼散射的背景存在，尽管产量较低，但由于其光稳定性而已被用于新颖的传感和成像应用。尽管表面等离子体激元作为增强天线的作用已被广泛接受，但关于发射机制的主要争议是将其分配给热载流子的辐射复合（光致发光）或电子拉曼散射（非弹性光散射）。我们之前将金纳米棒的斯托克斯位移发射解释为珀塞尔效应增强了热载流子的辐射复合。在这里，我们特别关注不同纵横比的单金纳米棒的反斯托克斯发射，激发波长低于和高于带间跃迁阈值，同时仍然采用连续波激光器。对斯托克斯和反斯托克斯发射之间的强度比的分析产生的温度只能解释为源自激发电子分布，而不是热平衡声子群，尽管没有使用脉冲激光激发。与这一结果以及之前使用超快激光器的发射研究一致，上转换发射的功率依赖性是非线性的，并且给出了参与光子的平均数量作为发射波长的函数。因此，我们的研究结果表明热载流子和光致发光在上转换发射中起着重要作用。
The origin of light emission from plasmonic nanoparticles has been strongly debated lately. It is present as the background of surface-enhanced Raman scattering and, despite the low yield, has been used for novel sensing and imaging applications because of its photostability. Although the role of surface plasmons as an enhancing antenna is widely accepted, the main controversy regarding the mechanism of the emission is its assignment to either radiative recombination of hot carriers (photoluminescence) or electronic Raman scattering (inelastic light scattering). We have previously interpreted the Stokes-shifted emission from gold nanorods as the Purcell effect enhanced radiative recombination of hot carriers. Here we specifically focused on the anti-Stokes emission from single gold nanorods of varying aspect ratios with excitation wavelengths below and above the interband transition threshold while still employing continuous wave lasers. Analysis of the intensity ratios between Stokes and anti-Stokes emission yields temperatures that can only be interpreted as Originating from the excited electron distribution and not a thermally equilibrated phonon population despite not using pulsed laser excitation. Consistent with this result as well as previous emission studies using ultrafast lasers, the power-dependence of the upconverted emission is nonlinear and gives the average number of participating photons as a function of emission wavelength. Our findings thus show that hot carriers and photoluminescence play a major role in the upconverted emission.