LAUSR

Perovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub‐nanosecond region, while sub‐nanosecond scintillators are highly demanded in various radiation detection, including high speed X‐ray imaging, time‐of‐flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb‐Br octahedral emitters in 2D organic‐inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr6]2− layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM2PbBr4. The emitting decay time is shortened as 0.97 ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190 photons MeV−1, which is greatly higher than conventional ultrafast scintillator BaF2 (1500 photons MeV−1). The rare combination of ultrafast decay time and considerable light yield renders BM2PbBr4 excellent performance in γ‐ray, neutron, α‐particle detection, and the best theoretical coincidence time resolution of 65.1 ps, which is only half of the reference sample LYSO (141.3 ps).