Temperature-dependent exciton dynamics and two-photon-induced localized exciton emission in CH(NH2)2PbBr3 single crystals

Understanding exciton recombination and exciton-phonon coupling in hybrid perovskite single crystals is essential for developing high-performance linear and nonlinear optoelectronic devices. Herein, we systematically investigate the photophysical processes in formamidinium lead bromide (CH(NH 2 ) 2 PbBr 3 ) single crystals through steady-state photoluminescence (PL), temperature-dependent spectroscopy, time-resolved PL, and Raman analysis. Under 405 nm excitation, dual emission peaks at 555 and 577 nm are assigned to free exciton (FE) and bound exciton (BE) recombination. Time-resolved PL measurements reveal nanosecond-scale lifetimes for FE and longer sub-microsecond lifetimes for BE. Under 800 nm excitation, a single 567 nm emission with a microsecond lifetime is observed, demonstrating two-photon absorption (2PA) induced localization and reabsorption-mediated relaxation. Temperature-dependent PL reveals an activation energy of 72 meV derived from Arrhenius fitting, while the monotonic linewidth broadening is well described by the Boson model with a longitudinal optical phonon energy of 24 meV. An anomalous evolution of the emission features around ∼160 K suggests a possible phase transition, which modulates exciton-phonon coupling and recombination dynamics. Raman spectroscopy further confirms strong electron-phonon interaction and lattice anharmonicity. These results establish a unified picture of FE-BE competition and 2PA-dominated recombination dynamics in CH(NH 2 ) 2 PbBr 3 , providing fundamental insight for perovskite-based lasers, nonlinear photonics, and scintillation devices.