Phonon-assisted upconversion in twisted two-dimensional semiconductors

Yuchen Dai; Pengfei Qi; Guangyi Tao; Guangjie Yao; Beibei Shi; Zhixin Liu; Zhengchang Liu; Xiao He; Pu Peng; Zhibo Dang; Liheng Zheng; Tianhao Zhang; Yongji Gong; Yan Guan; Kaihui Liu; Zheyu Fang

doi:10.1038/s41377-022-01051-9

Phonon-assisted upconversion in twisted two-dimensional semiconductors

Light Sci Appl. 2023 Jan 2;12(1):6. doi: 10.1038/s41377-022-01051-9.

Authors

Yuchen Dai^#¹, Pengfei Qi^#^{1

2}, Guangyi Tao^#^{1

3}, Guangjie Yao¹, Beibei Shi¹, Zhixin Liu¹, Zhengchang Liu¹, Xiao He¹, Pu Peng¹, Zhibo Dang¹, Liheng Zheng¹, Tianhao Zhang³, Yongji Gong⁴, Yan Guan⁵, Kaihui Liu¹, Zheyu Fang⁶

Affiliations

¹ School of Physics, State Key Laboratory for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, 100871, Beijing, China.
² Institute of Modern Optics, Nankai University, Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, 300350, Tianjin, China.
³ Photonics Research Center, School of Physics, MOE Key Lab of Weak-Light Nonlinear Photonics, and Tianjin Key Lab of Photonics Materials and Technology for Information Science, Nankai University, 300071, Tianjin, China.
⁴ School of Materials Science and Engineering, Beihang University, 100191, Beijing, China.
⁵ Center for Physicochemical Analysis and Measurements in ICCAS, Analytical Instrumentation Center, Peking University, 100871, Beijing, China.
⁶ School of Physics, State Key Laboratory for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, 100871, Beijing, China. zhyfang@pku.edu.cn.

^# Contributed equally.

Abstract

Phonon-assisted photon upconversion (UPC) is an anti-Stokes process in which incident photons achieve higher energy emission by absorbing phonons. This letter studies phonon-assisted UPC in twisted 2D semiconductors, in which an inverted contrast between UPC and conventional photoluminescence (PL) of WSe₂ twisted bilayer is emergent. A 4-fold UPC enhancement is achieved in 5.5° twisted bilayer while PL weakens by half. Reduced interlayer exciton conversion efficiency driven by lattice relaxation, along with enhanced pump efficiency resulting from spectral redshift, lead to the rotation-angle-dependent UPC enhancement. The counterintuitive phenomenon provides a novel insight into a unique way that twisted angle affects UPC and light-matter interactions in 2D semiconductors. Furthermore, the UPC enhancement platform with various superimposable means offers an effective method for lighting bilayers and expanding the application prospect of 2D stacked van der Waals devices.