Metal-halide perovskites have recently emerged as a promising platform for ultrafast scintillators owing to their high light yield and short emission lifetimes [1]. Our recent advances in in the field have demonstrated that coupling perovskite scintillators with plasmonic nanoantennas enables Purcell-enhanced radiative recombination, leading to brighter and faster scintillation, while subsequent studies extended these concepts toward exciton–plasmon strong coupling in bulk nanoplasmonic scintillators [2-4]. Building upon these developments, we investigate whether the geometry of plasmonic nanostructures can itself serve as a design parameter governing the transition from enhanced spontaneous emission to coherent light–matter interactions in different classes of perovskite scintillators.

To address this question, two representative perovskite emitters exhibiting distinct electronic structures, CsPbBr₃ and CsCu₂I₃, were co-dispersed with shape-controlled gold nanoparticles within a polymer matrix to form a composite slab. Gold octahedra and rhombic dodecahedra with sizes ranging from 40 to 90 nm were synthesized and further characterized spectroscopically and structurally. Their localized surface plasmon resonances were continuously tuned between 450 and 650 nm, enabling systematic control over the spectral overlap between plasmonic and excitonic transitions. The optical response was investigated using steady-state photoluminescence (PL), time-resolved PL (TRPL) allowing direct correlation between plasmonic resonance conditions and scintillation dynamics.

For CsPbBr₃ composites, rhombic dodecahedral Au nanoparticles with plasmon resonance centred at 545 nm induced the strongest impact on emission dynamics. At room temperature, nearly ninefold acceleration of the PL decay demonstrates highly efficient plasmon-assisted radiative rate engineering. Upon cooling below 180 K, where excitonic dephasing is significantly reduced, the system evolves into the strong-coupling regime, giving rise to pronounced Rabi splitting accompanied by a 2.5-fold enhancement of the PL intensity [3-4]. Simultaneously, the emission lifetime increases by approximately six times relative to room temperature, reflecting modified exciton relaxation dynamics associated with the formation of hybrid exciton–plasmon states.

In contrast, CsCu₂I₃ exhibits a distinctly different coupling behaviour despite being investigated within the same plasmonic platform. Strong exciton–plasmon coupling is observed exclusively for octahedral Au nanoparticles when their localized surface plasmon resonance spectrally coincides with the broadband emission centred near 600 nm. Under these resonance conditions, a pronounced Rabi splitting is accompanied by an approximately 2.5-fold enhancement of the PL intensity. Rhombic dodecahedra of comparable dimensions do not exhibit splitting despite similar spectral tuning, demonstrating that spectral overlap alone is insufficient to induce coherent coupling. We attribute this behaviour to the geometry-dependent electromagnetic near-field distribution, where the sharp edges of octahedral nanoparticles generate highly localized plasmonic hot spots, substantially strengthening the local optical field and exciton–plasmon interaction [5].

We demonstrate that the evolution from Purcell-enhanced emission to coherent exciton–plasmon coupling is governed not only by spectral resonance but also by the geometry of plasmonic nanostructures and the intrinsic properties of the emitting material. Our findings establish shape-selective plasmonic engineering as a new design principle for perovskite scintillators for future of ultrafast, high-light-yield detectors.