Characterizing the Nonlinear Optical Properties of CsPbBr₃ Nanocrystals Using Two-Beam Action Spectroscopy and Nonlinear Fluorescence Excitation

Halide perovskites have gained considerable attention in recent years due to their potential as easily processable and efficient photovoltaic materials. These materials also exhibit efficient multiphoton absorption (MPA). However, the characterization of MPA in halide perovskites has led to many conflicting reports. Here we apply a technique that we recently developed, two-beam constant emission intensity (2-BCEIn) spectroscopy, to the study of MPA-generated emission in CsPbBr₃nanocrystals. 2-BCEIn allows for the measurement of the order(s) of nonlinear absorption without requiring high dynamics range, allowing us to elucidate the photophysics of multiphoton excitation in this system. We also demonstrate that this material undergoes efficient MPA even with continuous-wave light at 800 nm.