Research Article


2022, 15(1): 326–332


Fast electrochemical activation of the broadband saturable absorption of tungsten oxide nanoporous film

Ruipeng Hou1, Hui Li1, Mengjuan Diao1, Yanhui Sun1, Ying Liang1, Zhiyang Yu2, Zhipeng Huang1 (✉), and Chi Zhang1 (✉)

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1 School of Chemical Science and Engineering, Tongji University, Shanghai 200092, China
2 State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou 350002, China

Keywords: tungsten oxide, nonlinear absorption, in-gap states, electrochemical activation
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The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable, while it remains a great challenge. In this work, we demonstrate that electrochemical activation is a facile and convenient approach to modulating the broadband third-order nonlinear absorption of nanoporous tungsten oxide (WO3–x) thin film. The film does not exhibit optical nonlinearity at the initial state, while shows a distinct saturable absorption under an applied voltage of –2.5 V with the excitation of 515, 800, and 1,030 nm laser. The nonlinear absorption coefficient (βeff) is –766.38 ± 6.67 cm·GW–1 for 1,030 nm laser, –624.24 ± 17.15 cm·GW–1 for 800 nm laser, and –120.70 ± 11.49 cm·GW–1 for 515 nm laser, and the performance is competitive among inorganic saturable absorbers. The activation is accomplished in 2 min. The performance enhancement is ascribed to the formation of abundant in-gap defect states because of the reduction of the tungsten atoms, and a Pauli-blocking effect occurs during the excitation of in-gap defect states. The small feature size of WO3–x (~ 12 nm) enables the effective and fast introduction and removal of the defects in porous film, and accordingly the fast and broadband modulation of optical nonlinearity. Our results suggest a controllable, effective, and convenient approach to tuning the nonlinear absorption of materials.
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Fast electrochemical activation of the broadband saturable absorption of tungsten oxide nanoporous film. Nano Res. 2022, 15(1): 326–332

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