Outstanding nonlinear optical properties of all-inorganic perovskite CsPbX (X=Cl, Br, I) precursor solutions and polycrystalline films.

In this work, we systematically explore the third-order nonlinear optical properties of all-inorganic CsPbX (X = Cl, Br, I) perovskite precursor solutions and thin films using femtosecond and nanosecond laser pulses. We show that these samples possess strong two-photon absorption (TPA) and reverse saturable absorption (RSA), which depend on the excitation wavelength. The obtained nonlinear absorption and refraction coefficients for precursor solutions are followed by the relation CsPbCl > CsPbBr > CsPbI for the 800 and 1,064 nm excitation wavelengths, whereas this relation became reverse in the case of 355 and 400 nm laser pulses. It was shown that CsPbCl thin film possesses RSA at 400 nm, CsPbCI shows RSA+ saturable absorption (SA), and CsPbBr demonstrates SA + RSA. In addition, at 800 nm excitation, the CsPbBr thin films show SA + RSA at low peak intensity, and the absorption becomes reverse (TPA+SA) with a further increase in the input laser intensity. The suitability of nonlinear absorption depends on the band gap of the thin films with respect to the pumping photon energy. Our studies demonstrate that these perovskites can be used as the excellent materials for the all-optical signal processing.