Giant anomalous exciton-multiphoton nonlinearities in layered hybrid perovskites.

Directly full-color frequency-upconversion under high-order multiphoton absorption (MPA) nonlinearities in NIR-III (1550-1870 nm) and NIR-IV (2100-2300 nm) windows is highly desirable for advanced photonics and bioimaging. However, it has remained beyond the reach of current materials due to their inherently weak high-order MPA. Here, we demonstrate that, driven by Bloch oscillations of excitonic dipoles after nonlinear polarization, giant multiphoton nonlinearities can be achieved in layered hybrid perovskites to enable full-color upconversion in NIR-III/IV windows. The MPA cross-section values of the designed three Ruddlesden-Popper perovskites are found to be several orders of magnitude larger than those of the reported MPA materials. These advancements facilitate versatile applications previously inaccessible in NIR-III/IV windows, including full-color upconversion displays and multicolor information encryption. Our work highlights the prospect of efficient high-order MPA and opens avenues for investigating excitonic quantum dynamics in high-order nonlinear optics.