Niihori Yoshiki, Kosaka Taiga, Negishi Yuichi
Research Institute for Science and Technology, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
Graduate School of Science, Department of Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
Mater Horiz. 2024 May 20;11(10):2304-2322. doi: 10.1039/d4mh00117f.
The phenomenon of photon upconversion (UC), generating high-energy photons from low-energy photons, has attracted significant attention. In particular, triplet-triplet annihilation-based UC (TTA-UC) has been achieved by combining the excitation states of two types of molecules, called the sensitizer and emitter (or annihilator). With TTA-UC, it is possible to convert weak, incoherent near-infrared (NIR) light, which constitutes half of the solar radiation intensity, into ultraviolet and visible light that are suitable for the operation of light-responsive functional materials or devices such as solar cells and photocatalysts. Research on TTA-UC is being conducted worldwide, often employing materials with high intersystem crossing rates, such as metal porphyrins, as sensitizers. This review summarizes recent research and trends in triplet energy transfer and TTA-UC for semiconductor nanoparticles or nanocrystals with diameters in the nanometer range, also known as quantum dots, and for ligand-protected metal nanoclusters, which have even smaller well-defined sub-nanostructures. Concerning nanoparticles, transmitter ligands have been applied on the surface of the nanoparticles to efficiently transfer triplet excitons formed inside the nanoparticles to emitters. Applications are expanding to solid-state UC devices that convert NIR light to visible light. Additionally, there is active research in the development of sensitizers using more cost-effective and environmentally friendly elements. Regarding metal nanoclusters, methods have been established for the evaluation of excited states, deepening the understanding of luminescent properties and excited relaxation processes.
光子上转换（UC）现象，即从低能光子产生高能光子，已引起了广泛关注。特别是，基于三重态-三重态湮灭的上转换（TTA-UC）已通过结合两种分子（称为敏化剂和发射体（或湮灭剂））的激发态得以实现。利用TTA-UC，可以将构成太阳辐射强度一半的微弱、非相干近红外（NIR）光转换为适用于光响应功能材料或器件（如太阳能电池和光催化剂）运行的紫外光和可见光。全球范围内都在开展关于TTA-UC的研究，通常使用具有高系间窜越率的材料（如金属卟啉）作为敏化剂。本综述总结了针对直径在纳米范围内的半导体纳米颗粒或纳米晶体（也称为量子点）以及具有更小、定义明确的亚纳米结构的配体保护金属纳米团簇的三重态能量转移和TTA-UC的最新研究及趋势。关于纳米颗粒，已在纳米颗粒表面应用了传输配体，以有效地将纳米颗粒内部形成的三重态激子转移至发射体。应用正在扩展到将近红外光转换为可见光的固态上转换器件。此外，在使用更具成本效益和环境友好型元素开发敏化剂方面也有积极的研究。关于金属纳米团簇，已建立了评估激发态的方法，加深了对发光特性和激发弛豫过程的理解。
