Nonlinear Optical Properties of Colloidal Perovskite Nanocrystals

Colloidal perovskite nanocrystals (PNCs) have been explored in the last years because of their remarkable linear optical properties, such as high photoluminescence quantum yield, narrow emission spectra, and high tunability in the visible range. Most recently, several reports have claimed that this class of nanomaterials also possesses outstanding third-order nonlinear optical properties, such as high two-photon absorption cross-section and high nonlinear refractive index. In this work, we investigate the size dependence of the nonlinear optical response in a series of cubic-shaped CsPbBr3 PNCs and show that their nonlinear optical response is not particularly high. Different from what it has been claimed in the literature, we show that no experimental evidence that supports the claim that the nonlinear refractive index for these PNCs is larger than those observed for other semiconductors. When all possible sources of artifacts are eliminated from the results, we observe that the measured magnitude of the intrinsic nonlinear refractive index varies between 10^-14 and 10^-13 cm²/W, the same order of magnitude obtained for bulk semiconductors with similar bandgap energy. Differently from isolated PNCS, we show that, when grouped in superlattices, these nanomaterials can present unique nonlinear optical response due to collective effects.<br/>Acknowledgements: FAPESP and CAPES.