Controlling the Crystallinity and Morphology of Bismuth Selenide via Electrochemical Exfoliation for Tailored Reverse Saturable Absorption and Optical Limiting

As an emerging two-dimensional (2D) Group-VA material, bismuth selenide (Bi₂Se₃) exhibits favorable electrical and optical properties. Here, three distinct morphologies of Bi₂Se₃ were obtained from bulk Bi₂Se₃ through electrochemical intercalation exfoliation. And the morphologies of these nanostructures can be tuned by adjusting solvent polarity during exfoliation. Then, the nonlinear optical and absorption characteristics of the Bi₂Se₃ samples with different morphologies were investigated using open-aperture Z-scan technology. The results reveal that the particle structure of Bi₂Se₃ exhibits stronger reverse saturable absorption (RSA) than the sheet-like structure. This is attributed to the higher degree of oxidation and greater number of localized defect states in the particle structure than in the sheet-like structure. Electrons in these defect states can be excited to higher energy levels, thereby triggering excited-state and two-photon absorption, which strengthen RSA. Finally, with increasing the RSA, the optical limiting threshold of 2D Bi₂Se₃ can also be increased. This work expands the potential applications of 2D Bi₂Se₃ materials in the field of broadband nonlinear photonics.