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An AIE organic zinc chloride complex scintillator, in which the metal halide serves as X-ray sensitizer for the organic component, is discovered to exhibit a light yield of 13 423 Photon per MeV and a radioluminescence decay lifetime of 5.24 ns. 

Abstract Highly sensitive stimuli‐responsive luminescent materials are crucial for applications in optical sensing, security, and anticounterfeiting. Here, we report two zero‐dimensional (0D) copper(I) halides, (TEP)₂Cu₂Br₄, (TEP)₂Cu₄Br₆, and 1D (TEP)₃Ag₆Br₉, which are comprised of isolated [Cu₂Br₄]²⁻, [Cu₄Br₆]²⁻, and [Ag₆Br₉]³⁻polyanions, respectively, separated by TEP⁺(tetraethylphosphonium [TEP]) cations. (TEP)₂Cu₂Br₄and (TEP)₂Cu₄Br₆demonstrate greenish‐white and orange‐red emissions, respectively, with near unity photoluminescence quantum yields, while (TEP)₃Ag₆Br₉is a poor light emitter. Optical spectroscopy measurements and density‐functional theory calculations reveal that photoemissions of these compounds originate from self‐trapped excitons due to the excited‐state distortions in the copper(I) halide units. Crystals of Cu(I) halides are radioluminescence active at room temperature under both X‐ and γ‐rays exposure. The light yields up to 15,800 ph/MeV under 662 keV γ‐rays of¹³⁷Cs suggesting their potential for scintillation applications. Remarkably, (TEP)₂Cu₂Br₄and (TEP)₂Cu₄Br₆are interconvertible through chemical stimuli or reverse crystallization. In addition, both compounds demonstrate luminescence on‐off switching upon thermal stimuli. The sensitivity of (TEP)₂Cu₂Br₄and (TEP)₂Cu₄Br₆to the chemical and thermal stimuli coupled with their ultrabright emission allows their consideration for applications such as solid‐state lighting, sensing, information storage, and anticounterfeiting.