Increased Intraband Transitions in Smaller Gold Nanorods Enhance Light Emission
Increased Intraband Transitions in Smaller Gold Nanorods Enhance Light Emission
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DOI：
10.1021/acsnano.0c06771
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发表时间：
2020-11-24
期刊：
影响因子：
17.1
通讯作者：
Link, Stephan
中科院分区：
文献类型：
--
作者：
Ostovar, Behnaz;Cai, Yi-Yu;Link, Stephan
等离子体纳米颗粒的光致发光因其在传感、成像和纳米测温方面的潜在应用而引起了科学界的极大兴趣。等离激元纳米粒子的光发射的建议机制之一是通过带间和带内跃迁的等离激元增强热载流子的辐射复合。在这里，我们通过对具有相似纵横比的金纳米棒进行系统分析，研究纳米颗粒尺寸对光致发光的依赖性。使用单粒子发射和散射光谱以及相关扫描电子显微镜和电磁模拟，我们计算了单个金纳米棒的发射量子产率和珀塞尔增强因子。我们的结果显示金纳米棒的量子产率具有很强的尺寸依赖性，较小的金纳米棒具有更高的量子产率。此外，通过确定带间和带内跃迁对光致发光的相对贡献，我们推断观察到的尺寸依赖性主要源自带内跃迁的尺寸依赖性。具体来说，在受激电荷载流子辐射复合的费米黄金法则的框架内，我们证明单独的珀塞尔因子增强不能解释发射尺寸依赖性，并且过渡矩阵元素的变化也必须发生。这些变化是由于电场限制增强了带内跃迁。这些结果为金属纳米限制系统中的带内弛豫提供了重要的见解，因此对于快速发展的等离子体光催化领域具有直接重要意义。
Photoinduced light emission from plasmonic nanoparticles has attracted considerable interest within the scientific community because of its potential applications in sensing, imaging, and nanothermometry. One of the suggested mechanisms for the light emission from plasmonic nanoparticles is the plasmon-enhanced radiative recombination of hot carriers through inter- and intraband transitions. Here, we investigate the nanoparticle size dependence on the photoluminescence through a systematic analysis of gold nanorods with similar aspect ratios. Using single-particle emission and scattering spectroscopy along with correlated scanning electron microscopy and electromagnetic simulations, we calculate the emission quantum yields and Purcell enhancement factors for individual gold nanorods. Our results show strong size-dependent quantum yields in gold nanorods, with higher quantum yields for smaller gold nanorods. Furthermore, by determining the relative contributions to the photoluminescence from interand intraband transitions, we deduce that the observed size dependence predominantly originates from the size dependence of intraband transitions. Specifically, within the framework of Fermi's golden rule for radiative recombination of excited charge carriers, we demonstrate that the Purcell factor enhancement alone cannot explain the emission size dependence and that changes in the transition matrix elements must also occur. Those changes are due to electric field confinement enhancing intraband transitions. These results provide vital insight into the intraband relaxation in metallic nanoconfined systems and therefore are of direct importance to the rapidly developing field of plasmonic photocatalysis.