Large third-order optical nonlinearities of two-dimensional CsPbBr₃ nanoplatelets

Metal halide perovskites show considerable optical nonlinearity and could be used for cost-effective nonlinear optical devices if their nonlinear susceptibilities can be improved. Here, we report large optical nonlinearity, including third-order nonlinear absorption, refraction, and two-photon absorption excited luminescence, of CsPbBr₃ nanoplatelets with a thickness of two or three atomic layers and a plane size of about 60 nm. Specifically, the nonlinear absorption was mainly induced by two-photon absorption at low incident powers, and the nonlinear absorption cross section reached 2.15 × 10⁷ GM. It is two orders of magnitude larger than that of CsPbBr₃ nanocrystals, which makes them an ideal optical limiting material. Furthermore, the nanoplatelets exhibited large self-phase modulation-induced nonlinear refraction, and the figures of merit W and T satisfied W >1 and T <1, which allow for optical switching. The large optical nonlinearity of CsPbBr₃ nanoplatelets provides a basis for multifunctional applications in nonlinear optical devices.