Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright

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 () and Akshay Rao ()
Additional contact information
Sanyang Han: University of Cambridge
Renren Deng: University of Cambridge
Qifei Gu: University of Cambridge
Limeng Ni: University of Cambridge
Uyen Huynh: University of Cambridge
Jiangbin Zhang: University of Cambridge
Zhigao Yi: National University of Singapore
Baodan Zhao: University of Cambridge
Hiroyuki Tamura: The University of Tokyo
Anton Pershin: University of Mons
Hui Xu: Heilongjiang University
Zhiyuan Huang: University of California, Riverside
Shahab Ahmad: Indian Institute of Technology Jodhpur
Mojtaba Abdi-Jalebi: University of Cambridge
Aditya Sadhanala: University of Cambridge
Ming Lee Tang: University of California, Riverside
Artem Bakulin: Imperial College London
David Beljonne: University of Mons
Xiaogang Liu: National University of Singapore
Akshay Rao: University of Cambridge

Nature, 2020, vol. 587, issue 7835, 594-599

Abstract: 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 coupling9–11 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.

Date: 2020
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DOI: 10.1038/s41586-020-2932-2

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