Ostovar Behnaz, Cai Yi-Yu, Tauzin Lawrence J, Lee Stephen A, Ahmadivand Arash, Zhang Runmin, Nordlander Peter, Link Stephan
ACS Nano. 2020 Nov 24;14(11):15757-15765. doi: 10.1021/acsnano.0c06771. Epub 2020 Sep 2.
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 inter- and 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.
由于等离激元纳米粒子的光致发光在传感、成像和纳米温度测量等领域具有潜在应用，其已在科学界引起了广泛关注。等离激元纳米粒子发光的一种可能机制是通过带间和带内跃迁实现热载流子的等离激元增强辐射复合。在此，我们通过对具有相似纵横比的金纳米棒进行系统分析，研究了纳米粒子尺寸对光致发光的影响。利用单粒子发射和散射光谱，结合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。我们的结果表明，金纳米棒的量子产率强烈依赖于尺寸，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于带内跃迁的尺寸依赖性。具体而言，在费米黄金定则框架下，对于激发电荷载流子的辐射复合，我们证明仅珀塞尔因子增强无法解释发射尺寸依赖性，跃迁矩阵元也必定发生了变化。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受限系统中的带内弛豫提供了重要见解，因此对于快速发展的等离激元光催化领域具有直接重要性。
