Giant two- to five-photon absorption in CsPbBr27I03 two-dimensional nanoplatelets

CsPbBr2.7I0.3 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.