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J Phys Chem Lett. 2019 Mar 21;10(6):1251-1258. doi: 10.1021/acs.jpclett.9b00524. Epub 2019 Mar 4.

Optical Gain from Biexcitons in CsPbBr3 Nanocrystals Revealed by Two-dimensional Electronic Spectroscopy.

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Department of Physics , Tsinghua University , Beijing 100084 , China.
National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing 210093 , China.
Department of Physics , University of Arkansas , Fayetteville , Arkansas 72701 , United States.


Perovskite semiconductor nanocrystals (NCs) exhibit highly efficient optical gain, which is promising for laser applications. However, the intrinsic mechanism of optical gain in perovskite NCs, particularly whether more than one exciton per NCs is required, remains poorly understood. Here, we use two-dimensional electronic spectroscopy to resonantly probe the interplay between near-band-edge transitions during the buildup of optical gain in CsPbBr3 NCs. We find compelling evidence to conclude that optical gain in CsPbBr3 NCs is generated through stimulated emission from strongly interacting biexcitons. The threshold is largely determined by the competition between stimulated emission from biexcitons and excited-state absorption from single exciton to biexciton states. The findings in this work may guide future explorations of NC materials with low-threshold optical gain.

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