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 multication 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.