Fig. 3. Two-photon excited fluorescence in MAPbBr₃ crystal and single-photon excited optical properties of cleaved crystal surface.

(A) 2D pseudocolor plot of two-photon (800 nm) excited TRPL measured in air. (B) TRPL dynamics [extracted from measurement reported in (A)]; the fit gives lifetimes of t₁ = 34 ns and t₂ = 4.5 μs. Inset: Image of MAPbBr₃ crystal under two-photon excitation (TPE) with an excitation wavelength of 800 nm. (C) Two-photon excited PL spectra measured in air and vacuum. (D) 2D pseudocolor plot of TRPL of a freshly cleaved crystal in air; the excitation wavelength is 400 nm. The emission peak wavelength as a function of time is indicated by the red line. (E) Calculated photocarrier density profile at various times under 400-nm laser excitation. Inset: Image of MAPbBr₃ crystal under single-photon excitation (SPE) with an excitation wavelength of 400 nm. (F) Calculated PL spectra at various times after excitation.