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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. 

Abstract Herein, a new family of hybrid metal halides, (DMAP)₂MBr₄(M = Cu, Zn), featuring zero‐dimensional (0D), pseudo‐layered crystal structures containing isolated molecular 4‐dimethylaminopyridinium (DMAP, C₇H₁₁N₂⁺) cations and MBr₄²⁻tetrahedral anions are reported. (DMAP)₂MBr₄show remarkable long‐term stability, with no signs of degradation after one year of ambient air exposure. The reported solution synthesis affords large crystals measuring up to 1 cm, which showed significant response to soft 8 keV X‐ray photons when implemented into X‐ray detectors. Furthermore, (DMAP)₂ZnBr₄demonstrates tunable color light emission properties, which is attributed to the organic molecular units based on our combined experimental and computational results. The measured photoluminescence quantum yield (PLQY) for (DMAP)₂ZnBr₄is 7.35 %, a remarkable enhancement of emission efficiency as compared to a weak emission from the organic precursor. The inexpensive and earth‐abundant chemical compositions and ease of preparation of the new hybrid metal halides make them promising candidates for optical and electronic applications. 

Abstract Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue‐emitting all‐inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A₂AgX₃(A = Rb, Cs; X = Cl, Br, I) through solid‐state synthesis is reported. In contrast to the Cu(I) analogs, A₂AgX₃are broad‐band emitters sensitive to A and X site substitutions. First‐principle calculations show that defect‐bound excitons are responsible for the observed main PL peaks in Rb₂AgX₃and that self‐trapped excitons (STEs) contribute to a minor PL peak in Rb₂AgBr₃. This is in sharp contrast to Rb₂CuX₃, in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A₂AgX₃significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A₂AgX₃are prepared and successfully used in anti‐counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A₂AgX₃suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications. 

This review clarifies the confusion regarding similarities and differences between the photoluminescent hybrid organic–inorganic and coordination Cu(i) halides, including their crystal and electronic structures, and optical properties. 

All‐inorganic copper(I) halides have recently emerged as attractive alternatives to lead‐based halide perovskites and rare‐earth‐doped inorganics for light emission applications. Most of the newly discovered all‐inorganic Cu(I) halides demonstrate high‐efficiency blue emission albeit with unusually poor tunability of photoluminescence (PL) properties. This work reports the facile preparation of three new copper(I) halides based on the guanidinium cation: (CN₃H₆)₃CuCl₄, (CN₃H₆)₇Cu₃Br₁₀·3(C₃H₇NO), and (CN₃H₆)₇Cu₃I₁₀·3(C₃H₇NO). A comprehensive characterization of PL is presented for these novel materials, which have highly tunable, dual blue–yellow emission responsive to both excitation wavelength and vacuum annealing. These have remarkable photoluminescence quantum yield (PLQY) values of up to 34.6% and color‐rendering indices (CRI) up to 97% for tunable, single‐phase white light emission with correlated color temperatures (CCT) ranging from 4851 to 18 921 K, demonstrating the excellent potential of Cu(I) halides for light emission applications.