Ultrafast scintillation is a central requirement for next-generation time-of-flight positron emission tomography (ToF-PET), collider calorimetry, and high-rate particle tracking, yet virtually all commercial scintillators still funnel deposited energy into incoherent recombination of localized carriers. This structural bottleneck enforces a long-standing trade-off between light yield, timing, and spectral self-absorption in direct emitters, and prevents the use of quantum-coherent observables in radiation detection. Here we report a route beyond this limit by harnessing cooperative emission in quantum-ordered lead-halide perovskite nanocrystal (NC) superlattices (SLs), and by demonstrating, for the first time, superfluorescence (SF) directly triggered by ionizing radiation.

Our platform consists of highly monodisperse CsPbBr₃ NCs self-assembled into long-range ordered SLs, forming large continuous domains with orientational locking and electronic coherence across many dots. Structural characterization by transmission electron microscopy and electron diffraction confirms the cubic NC lattice and the mesoscale order required for cooperative light-matter coupling. We first establish the emergence of SF under optical excitation through ps-fast streak camera measurements, observing the delayed build-up of a narrow, red-shifted emission band whose intensity and lifetime follow the expected fluence- and temperature-dependent cooperative scaling. These signatures confirm that the SLs support macroscopic polarization and collective radiative decay over coherence volumes encompassing many NCs.

We then probe scintillation under X-ray excitation. Strikingly, the radioluminescence (RL) from the SLs is dominated (>90%) by a superfluorescent collective state, yielding bright picosecond photon bursts with effective scintillation lifetimes as short as ~40 ps at 20 K and persisting with minimal degradation up to and beyond the technological cornerstone of 80 K for nitrogen-based cryogenics. From second-order correlation (g²) kinetics we extract the ~40 ps timescale, placing SF scintillation among the fastest radiative responses reported under ionizing excitation. Crucially, SF emission is red-shifted by ~60 meV from uncoupled NC emission and by up to ~100 meV from the SL absorption edge, effectively suppressing reabsorption even in dense architectures.

To connect these cooperative optical signatures to ionization physics, we perform Geant4 Monte-Carlo simulations of energy deposition in a SL. The simulations indicate that secondary electrons generated by high-energy X-photons localize deposited energy within close-packed NC tracks on length scales consistent with coherence volumes, providing a realistic pathway for stochastic ionization cascades to seed coherent many-body emission.

Together, these results position solution-processable perovskite NC superlattices as coherent scintillating metamaterials in which collective radiative decay sets the ionizing-radiation response, offering a practical route to ultrafast, reabsorption-free nanoscintillators compatible with metascintillator architectures and potentially enabling detector concepts sensitive not only to light yield but also to the timing and statistical structure of the emitted photons.