(Peer-Reviewed) Observation of polaronic state assisted sub-bandgap saturable absorption
Li Zhou 周莉 ¹, Yiduo Wang 王一多 ¹ ², Jianlong Kang 康建龙 ¹, Xin Li 李鑫 ¹, Quan Long 龙泉 ¹, Xianming Zhong 钟先明 ¹, Zhihui Chen 陈智慧 ¹, Chuanjia Tong 童传佳 ¹, Keqiang Chen 陈克强 ³, Zi-Lan Deng 邓子岚 ⁴, Zhengwei Zhang 张正伟 ¹, Chuan-Cun Shu 束传存 ¹, Yongbo Yuan 袁永波 ¹, Xiang Ni 倪祥 ¹, Si Xiao 肖思 ¹, Xiangping Li 李向平 ⁴, Yingwei Wang 王迎威 ¹, Jun He 何军 ¹
¹ Hunan Key Laboratory of Nanophotonics and Devices, School of Physics, Central South University, Changsha 410083, China
中国 长沙 中南大学物理学院 纳米光子学与器件湖南省重点实验室
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
中国 北京 中国科学院物理研究所 北京凝聚态物理国家实验室
³ Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, China
中国 北京 中国地质大学 材料与化学学院
⁴ Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Institute of Photonics Technology, College of Physics & Optoelectronic Engineering, Jinan University, Guangzhou 510632, China
中国 广州 暨南大学物理与光电工程学院 光子技术研究院 广东省光纤传感与通信技术重点实验室
Opto-Electronic Advances, 2025-06-19
Abstract
In soft-lattice lead-halide perovskites, the polaronic effects involving stabilization of localized charge character by structural deformations and polarizations have an important effect on the properties of functional materials such as the band gap, which has attracted considerable investigations. However, the concept of polaron assisted nonlinear photonics remains largely unexplored, which has a wide range of applications from optoelectronics to telecommunications and quantum technologies.
Here, we report the first observation of the polaronic state assisted saturable absorption through sub-bandgap excitation with a redshift exceeding 60 meV. By combining photoluminescence, transient absorption measurements and density functional theory calculations, we explicate that the anomalous nonlinear saturable absorption under sub-bandgap excitation is caused by the transient picosecond timescale polaronic state formed by strong carrier/exciton-phonon coupling effect.
The bandgap fluctuation caused by polaron formation can be further tuned through exciton-phonon coupling of perovskites with different Young’s modulus. This suggests that we can design targeted soft lattice lead-halide perovskite with a specific structure to effectively manipulate exciton-phonon coupling and exciton-polaron formation. These findings profoundly expand our understanding of exciton-polaronic nonlinear optics physics and provide an ideal platform for developing actively tunable nonlinear photonics applications.
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