Giant two- to five-photon absorption in CsPbBr_2.7I_0.3 two-dimensional nanoplatelets

CsPbBr_2.7I_0.3 two-dimensional (2D) nanoplatelets (NPs) with emission wavelengths of 469 nm and 527 nm were synthesized and characterized. Femtosecond transient absorption spectra revealed hot carrier cooling times of ∼368  fs and ∼438  fs for 469 nm and 527 nm 2D NPs, respectively. Importantly, the 2D NPs exhibit giant two-, three-, four-, and five-photon absorption cross-sections, reaching ∼4.1×10⁶ GM at 830 nm, ∼2.3×10^-74  cm⁶ s² photon^-2 at 1300 nm, 2.06×10^-104  cm⁸ s³ photon^-3 at 1600 nm, and 1.50×10^-136  cm¹⁰ s⁴ photon^-4 at 2200 nm, respectively, which are 3-8 orders of magnitude larger, compared to specially designed organic molecules.