Nonlinear absorption and temperature-dependent fluorescence of perovskite FAPbBr₃ nanocrystal

Recent progress in solar cell and light-emitting devices makes halide perovskite a research hot spot in optics. In this Letter, the nonlinear absorption and fluorescence properties of FAPbBr₃ nanocrystal, one typical organometallic halide perovskite, have been investigated via Z-scan measurements and a density-dependent photoluminescence (PL) spectrum. The FAPbBr₃ nanocrystal exhibits nonlinear absorption under the excitation of 800 nm, whose photon energy is below the bandgap of FAPbBr₃. The significant absorption is experimentally confirmed to be induced by two-photon absorption (TPA), and the TPA coefficient is measured to be ∼0.0042  cm/GW. Moreover, the PL induced by TPA in FAPbBr₃ nanocrystal shows different temperature-dependent behaviors in the range of 90 to 350 K. The peaks of the PL spectrum remain nearly constant at 100-160  K, with a very shallow trough at around 150 K, while a linear blue shift (0.496 meV/K) of the spectrum is observed when temperature is above 160 K. These temperature-dependent fluorescence behaviors can be ascribed to the structural phase transition at about 150 K and the contribution of thermal expansion. Moreover, the exciton binding energy around 160 meV and the optical phonon energy of 15.3 meV are also extracted from the temperature-dependent PL data.