Addressing the Magnitude of the Nonlinear Refraction Response in Perovskite Nanocrystals

Colloidal perovskite nanocrystals (PNCs) are among the most studied optical materials in the last decade. Because of their remarkable optical properties, such as high photoluminescence quantum yield, narrow emission spectra, and high tunability in the visible range, they have become important candidates for several applications in optoelectronics technologies. Most recently, several reports have claimed that this class of nanomaterials also possesses outstanding third-order nonlinear optical properties, such as a high two-photon absorption cross section and a high nonlinear refractive index. In this paper, we investigate the nonlinear optical response for a series of CsPbBr3 PNCs and show that their nonlinear optical response is not particularly high. Different from what has been claimed in the literature, we show that no evidence is found to support that the nonlinear refractive index for these PNCs is larger than those observed for other semiconductors, as the measured magnitude varies between 10-14 and 10-13 cm2/W, the same order of magnitude as bulk semiconductors with a similar band gap energy.