剑桥大学Akshay Rao团队通过镧掺杂无机纳米颗粒点亮三线态激子。该研究成果于2020年发表在国际顶尖学术期刊《自然》。

分子和杂化体系中的三线态激子的产生、控制和转移因其在在固态和溶液相中展现出长寿命和大扩散长度等特点及其在发光、光电以及光催化等领域的应用持续引发着人们的高度关注。然而，分子三线态激子（束缚电子-空穴对）是“暗态”，不能直接在自旋为零的基态和自旋为一的三线态之间直接发生光跃迁，通常只能通过重金属基自旋轨道耦合或者单-三线态分裂能等策略进行控制。这两种方法都限制了可修饰的性能和可使用的分子结构的范围。

该文中，研究人员证明了通过耦合有机分子和掺镧的无机绝缘纳米颗粒来控制三线态动力学是可能的。该策略允许传统的基态单线态-激发三线态的禁阻跃迁获得振子强度，从而使三线态可以通过光子吸收直接在分子上产生。光产生的单线态激子可在亚10皮秒时间尺度内转变成三线态激子，并且三线态激子在镧系离子的作用可进行能量转移，从而实现对暗三线态激子的发光富集。

此外，研究人员证明了由近红外光激发在稀土纳米颗粒-分子杂化系统中产生的三线态激子可以通过镧-三线态激发融合进行有效的上转换过程。该过程实现了吸热上转换，并允许固态频率从近红外到可见光的有效上转换。

该结果为控制三线态激子提供了一种新的方法，对于光电和生物医学领域的研究具有重要意义。

附：英文原文

Title: Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright

Author: Sanyang Han, Renren Deng, Qifei Gu, Limeng Ni, Uyen Huynh, Jiangbin Zhang, Zhigao Yi, Baodan Zhao, Hiroyuki Tamura, Anton Pershin, Hui Xu, Zhiyuan Huang, Shahab Ahmad, Mojtaba Abdi-Jalebi, Aditya Sadhanala, Ming Lee Tang, Artem Bakulin, David Beljonne, Xiaogang Liu, Akshay Rao

Issue&Volume: 2020-11-25

Abstract: The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission1, optoelectronics2,3, photon frequency conversion4,5 and photocatalysis6,7. Molecular triplet excitons (bound electron–hole pairs) are ‘dark states’ because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels8. Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin–orbit coupling9,10,11 or tuning of the singlet–triplet energy splitting12,13 via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle–molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide–triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research.

DOI: 10.1038/s41586-020-2932-2

Source: https://www.nature.com/articles/s41586-020-2932-2