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 (BiSe) exhibits favorable electrical and optical properties. Here, three distinct morphologies of BiSe were obtained from bulk BiSe 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 BiSe samples with different morphologies were investigated using open-aperture Z-scan technology. The results reveal that the particle structure of BiSe 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 BiSe can also be increased. This work expands the potential applications of 2D BiSe materials in the field of broadband nonlinear photonics.