Third-Order Optical Nonlinearities of Pristine and Manganese-Incorporated Bismuth Subcarbonate Nanostructures for Optical Limiters

High-intensity lasers have significant application fields in current technologies, posing a major challenge to safeguarding light-sensitive materials. Exploring third-order optical nonlinearities paves the way to finding suitable materials for the smart filtering of high-intensity optical radiation. Herein, we report the nonlinear absorption (β) properties of hydrothermally synthesized bismuth subcarbonate ((BiO) 2 CO 3 ) and manganese-incorporated bismuth subcarbonate (Mn:(BiO) 2 CO 3 ) nanostructures probed using the nanosecond laser-excitation-driven open aperture Z-scan technique. It is quite interesting that (BiO) 2 CO 3 exhibits a W-shaped nonlinear absorption profile owing to the coexistence of two-photon absorption and ground-state bleaching. In contrast to this, Mn:(BiO) 2 CO 3 displays reverse saturable absorption (RSA) suitable for optical limiting effects. The plausible mechanism behind the transition from a W-shaped nonlinear absorption profile to RSA is related to high surface charge carriers. Mn 2+ ion incorporation plays a tremendous role in the modifications of its morphology revealed by transmission electron microscopy (TEM) images. The optical limiting threshold was found to be 2.52 × 10 12 W/m 2 . The spatial electric field distribution of both samples was simulated by using the finite difference time domain (FDTD) method. The simulation results show that the localized electric field enhancement leads to a significant rise in nonlinear absorption, which agrees with the experimental Z-scan nonlinear transmittance analysis.