Strong Coupling in Bulk Nanoplasmonic Nanoplatelet Perovskite Scintillators

Control of light emission in solid materials underpins modern photonics and quantum technologies. Strong coupling between excitons and confined electromagnetic modes creates hybrid light–matter states of polaritons that enable fundamentally new optical functionalities. However, such coupling has so far been limited to nanoscale or ultrathin systems, precluding its use in bulk materials required for scintillation and radiation detection. Here, we demonstrate macroscopic exciton–plasmon strong coupling in lead-halide nanoplatelet perovskite composites embedded with silver nanocubes. By reducing nanocube dimensions to nanoplatelet and temperature tuning, we achieve precise resonance alignment between excitonic and plasmonic modes, revealing pronounced Rabi splitting and mode anticrossing. The measured coupling strength surpasses both excitonic and plasmonic losses, confirming operation deep in the strong-coupling regime. This work establishes a scalable route to bulk polaritonic materials, where scintillation yield and response speed can be engineered through light–matter hybridisation, opening pathways toward next-generation radiation detectors, medical imaging systems, and quantum photonic devices.