Abstract
ABSTRACT
Perovskite CsPbI
3
nanocrystals (NCs) hold tremendous promise as red‐emitting scintillators with high light yields and fast response, owing to their narrow bandgap, large effective atomic number, and superior emission efficiency. However, the scintillation capability of CsPbI
3
NC scintillators remains severely bottlenecked by inefficient radiation energy utilization. Beyond the well‐known optical losses (e.g., reabsorption, scattering, and concentration quenching), the mechanism of efficiently capturing secondary electrons (SEs) to maximize energy deposition inside NC remains largely unexplored. Herein, we report a hierarchical encapsulation strategy to construct superassembled CsPbI
3
NCs, delivering bright and fast scintillators. Multiexciton dynamic analysis reveals that the dense superassembled solids not only boost the SE capture efficiency but also increase the fraction of fast radiative biexcitons. Consequently, the superassembled NC scintillator achieves a light yield of 10 200 photons MeV
−1
and a radioluminescence (RL) decay time of 5.5 ns, yielding a record‐high light yield/decay time figure of merit of 1800 among all red‐emitting scintillators. Moreover, the hierarchical architecture successfully retards the phase transition of CsPbI
3
, imparting the nanoscintillators with an exceptional x‐ray radiation hardness up to 2300 Gy. This work provides profound physical insights into energy conversion and multiexciton engineering within dense architecture and paves an avenue toward next‐generation, high‐performance perovskite nanoscintillators.