Ultrafast Scintillation Enabled by Exciton Localization in High-Entropy Fluoride Crystals
Ultrafast scintillators with low-nanosecond emission are essential for next-generation high-rate X-ray and particle imaging. Although Ce3+-activated scintillators inherently exhibit fast response characteristics, conventional Ce3+-doped hosts rarely achieve low-nanosecond ultrafast decay. Here, we report a high-entropy fluoride scintillator (HEFS), Ce:LaGdCaSrBaF12 (Ce:LGCSB), in the form of bulk single crystals. The severe lattice distortion arising from multi-cation disorder induces exciton localization and effectively suppresses exciton diffusion. Through the rapid relaxation of localized excitons, the high-entropy Ce:LGCSB single crystals deliver a decay time of 1.23 ns with a 94.6% fast-component contribution and without any noticeable slow component. Through first-principles calculations, spectroscopic characterization, and transient dynamics analysis, we reveal that the ultrafast response originates from accelerated Frenkel exciton (FE) recombination enabled by the high-entropy environment. This work establishes entropy-engineered fluorides as promising ultrafast scintillator platforms and proposes a general strategy for extending sluggish diffusion effects to the excitonic scale, offering new opportunities for improving scintillation timing performance.