In Situ Growth of Stable (DPPM)₂Cu₄I₄@TPU Flexible Scintillator Films

Copper(I) halides are promising for X-ray scintillation owing to high luminescence and solution processability, but their poor stability limits practical use. Here we report a zero-dimensional coordinative cluster, (DPPM)₂Cu₄I₄ (DPPM = bis (diphenylphosphino) methane), prepared by a simple anti-solvent crystallization that emits bright orange light with an absolute photoluminescence quantum yield of 91.11%. Spectroscopic analysis (long lifetime, large Huang-Rhys factor) indicates self-trapped-exciton dominated radiative recombination. The cluster shows outstanding thermal (stable to ≈362 °C), solvent (stable after 30 d in H₂O, EA, EtOH, IPA) and air stability (>60 d), addressing common durability issues of copper(I) halides. Using an in situ growth method, microcrystals of (DPPM)₂Cu₄I₄ were uniformly incorporated into a thermoplastic polyurethane (TPU) matrix to form flexible scintillator films. The composite exhibits a high light yield of 17,064 photons MeV^-1 and a spatial resolution of 14 lp mm^-1, highlighting its great potential for practical X-ray imaging applications.