Scintillating Fibers From Stable Heteroleptic Hybrid Glasses for Remote X‑Ray Detection

Long‐distance and flexible optical fiber scintillators are essential under extreme operating conditions including interventional radiology and remote nuclear reactor monitoring, etc. Organic–inorganic hybrid glass fibers offer a promising solution, yet transforming cluster glasses into stable photonic architectures remains challenging. Here we report a heteroleptic strategy that exploits steric hindrance effects to precisely modulate the thermodynamic properties of hybrid Cu 4 I 4 cluster glass, further enabling ultralong, fracture‐free, and perturbation‐free TPP 2 MDP 2 Cu 4 I 4 (TPP = Triphenylphosphine; MDP = Methyldiphenylphosphine) glass fibers. The heteroleptic TPP 2 MDP 2 Cu 4 I 4 core glass not only overcomes the stability limitations of hybrid systems, but also exhibits a notable light yield of 38598 photons MeV −1 and a low detection limit of 62.2 nGy s −1 . We assemble these fibers into a flexible scintillation fiber array capable of imaging internal defects in confined spaces. This heteroleptic design principle in cluster glass platform can be extended to other hybrid glass fibers for emerging photonic applications.