Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright
Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright
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DOI：
10.1038/s41586-020-2932-2
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发表时间：
2020-11-26
期刊：
影响因子：
64.8
通讯作者：
Rao, Akshay
中科院分区：
文献类型：
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作者：
Han, Sanyang;Deng, Renren;Rao, Akshay
三重态激子在分子和混合系统中的产生、控制和转移引起了人们的极大兴趣，因为它们在固态和溶液相系统中都具有长寿命和扩散长度，并且在光发射(1)、光电子学(2,3)、光子频率转换(4,5)和光催化(6,7)中的应用。分子三重态激子（束缚电子空穴对）是“暗态”，因为自旋零基态和自旋一三重态能级之间直接光学跃迁的禁止性质(8)。因此，三重态动力学通常通过基于重金属的自旋轨道耦合(9-11)或通过分子设计调节单重态-三重态能量分裂(12,13)来控制。这两种方法都对可修改的性能范围和可使用的分子结构都有限制。在这里，我们证明可以通过将有机分子与镧系元素掺杂的无机绝缘纳米颗粒偶联来控制三重态动力学。这使得从基态单重态到激发态三重态的经典禁戒跃迁能够获得振荡器强度，从而能够通过光子吸收在分子上直接生成三重态。光生单线态激子可以通过系间窜越以统一效率在亚 10 皮秒时间尺度上转化为三线态激子。分子的三重态激子态可以以单位效率将能量转移到镧系离子，这使我们能够实现暗三重态激子的发光收获。此外，我们证明，通过近红外光激发在稀土纳米粒子-分子杂化系统中产生的三重态激子可以通过稀土-三重态激发聚变过程进行有效的上转换：该过程能够实现吸热上转换，并允许在固态下从近红外到可见频率的有效上转换。这些结果提供了一种控制三重态激子的新方法，这对于光电和生物医学研究的许多领域至关重要。
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 emission(1), optoelectronics(2,3,) photon frequency conversion(4,5) and photocatalysis(6,7). 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 levels(8). Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin-orbit coupling(9-11) or tuning of the singlet-triplet energy splitting(12,13) 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.