Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60–100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications.
Bibliographical noteFunding Information:
We acknowledge stimulating discussions with Xiaomu Wang, Yuerui Lu and Zongfu Yu. The work at Nanjing University is supported by National Natural Science Foundation of China 61734003, 61521001, 61851401, 51861145202, 61861166001, 21722302, 11874199; National Key Basic Research Program of China 2015CB921600; Strategic Priority Research Program of Chinese Academy of Sciences XDB 30000000; Key Laboratory of Advanced Photonic and Electronic Materials, Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics, and the Fundamental Research Funds for the Central Universities of China. The work at Southeast University is supported by National Key Research and Development of China 2017YFA0205700. The work at Chinese University of Hong Kong is supported by RGC of Hong Kong SAR under AoE/ P-03/08, CUHK Group Research Scheme. The optical measurement in Berkeley is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05CH11231 within the Electronic Materials Program (KC1201).
© 2019, The Author(s).
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)