Xu Jiahui, Dong Zhaogang, Asbahi Mohamed, Wu Yiming, Wang Hao, Liang Liangliang, Ng Ray Jia Hong, Liu Hailong, Vallée Renaud A L, Yang Joel K W, Liu Xiaogang
Department of Chemistry and The N.1 Institute for Health, National University of Singapore, Singapore 117543, Singapore.
Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Singapore 138634, Singapore.
Nano Lett. 2021 Apr 14;21(7):3044-3051. doi: 10.1021/acs.nanolett.1c00232. Epub 2021 Mar 9.
Efficient generation of anti-Stokes emission within nanometric volumes enables the design of ultracompact, miniaturized photonic devices for a host of applications. Many subwavelength crystals, such as metal nanoparticles and two-dimensional layered semiconductors, have been coupled with plasmonic nanostructures for augmented anti-Stokes luminescence through multiple-harmonic generation. However, their upconversion process remains inefficient due to their intrinsic low absorption coefficients. Here, we demonstrate on-chip, site-specific integration of lanthanide-activated nanocrystals within gold nanotrenches of sub-25 nm gaps via bottom-up self-assembly. Coupling of upconversion nanoparticles to subwavelength gap-plasmon modes boosts 3.7-fold spontaneous emission rates and enhances upconversion by a factor of 100 000. Numerical investigations reveal that the gap-mode nanocavity confines incident excitation radiation into nanometric photonic hotspots with extremely high field intensity, accelerating multiphoton upconversion processes. The ability to design lateral gap-plasmon modes for enhanced frequency conversion may hold the potential to develop on-chip, background-free molecular sensors and low-threshold upconversion lasers.
在纳米级体积内高效产生反斯托克斯发射，使得能够设计出用于众多应用的超紧凑、小型化光子器件。许多亚波长晶体，如金属纳米颗粒和二维层状半导体，已与等离子体纳米结构耦合，通过多谐波产生增强反斯托克斯发光。然而，由于其固有的低吸收系数，它们的上转换过程仍然效率低下。在此，我们通过自下而上的自组装，展示了在间隙小于25 nm的金纳米槽内进行镧系元素激活纳米晶体的片上、位点特异性集成。上转换纳米颗粒与亚波长间隙等离子体模式的耦合使自发发射率提高了3.7倍，并将上转换增强了100000倍。数值研究表明，间隙模式纳米腔将入射激发辐射限制在具有极高场强的纳米级光子热点中，加速了多光子上转换过程。设计横向间隙等离子体模式以增强频率转换的能力，可能具有开发片上、无背景分子传感器和低阈值上转换激光器的潜力。
