Defect-resolved energy relaxation and scintillation dynamics in two-dimensional halide perovskites

Two-dimensional (2D) halide perovskites are promising candidates for optoelectronics and radiation detection, yet they frequently exhibit anomalous behaviors including sub-theoretical light yields, negative thermal quenching (NTQ), long decay tails, and low-temperature spectral splitting. Here, we use single-crystalline 2D perovskites as a model system to systematically elucidate the role of intrinsic defects in governing energy relaxation and scintillation dynamics. By combining temperature-dependent spectroscopy, thermally stimulated luminescence, and theoretical calculations, we identify shallow donors associated with bromine vacancies (VBr) and deep acceptors linked to bromine interstitials (Bri) as the dominant trapping centers. Our analysis reveals that the reversible trapping of carriers by shallow VBr donors is responsible for the observed long decay tails and triggers NTQ upon thermal detrapping, which replenishes the band edge exciton population. Conversely, deep Bri acceptors facilitate donor–acceptor pair recombination responsible for the broad low-temperature emission while simultaneously acting as dominant non-radiative sinks that limit the absolute light yield. These findings establish a defect-resolved framework for understanding energy relaxation in 2D perovskites, providing insights to further mitigate intrinsic loss channels.