Zero-Dimensional Broadband Yellow Light Emitter (TMS)₃Cu₂I₅ for Latent Fingerprint Detection and Solid-State Lighting

We report a new hybrid organic-inorganic Cu(I) halide, (TMS)₃Cu₂I₅ (TMS = trimethylsulfonium), which demonstrates high efficiency and stable yellow light emission with a photoluminescence quantum yield (PLQY) over 25%. The zero-dimensional crystal structure of the compound is comprised of isolated face-sharing photoactive [Cu₂I₅]^3- tetrahedral dimers surrounded by TMS⁺ cations. This promotes strong quantum confinement and electron-phonon coupling, leading to a highly efficient emission from self-trapped excitons. The hybrid structure ensures prolonged stability and nonblue emission compared to unstable blue emission from all-inorganic copper(I) halides. Substitution of Cu with Ag leads to (TMS)AgI₂, which has a one-dimensional chain structure made of edge-sharing tetrahedra, with weak light emission properties. Improved stability and highly efficient yellow emission of (TMS)₃Cu₂I₅ make it a candidate for practical applications. This has been demonstrated through utilization of (TMS)₃Cu₂I₅ in white light-emitting diode with a high Color Rendering Index value of 82 and its use as a new luminescent agent for visualization of in-depth latent fingerprint features. This work illuminates a new direction in designing multifunctional nontoxic hybrid metal halides.