Optical properties of [MMim]2[CuI3] crystals with 0D single-core trigonal planar structures

In recent years, lead-free organic–inorganic hybrid zero-dimensional metal halides have attracted considerable attention due to their outstanding optical properties, largely attributed to the confinement of localized metal groups. We report the discovery of a newly structured [MMim]2[CuI3] crystal with a distinct [CuI3]2− trigonal planar structure encapsulated by inert organic [MMim]+ clusters. The structure, composition, and thermal stability of the crystal were analyzed using XRD and TG–DTA. The optical properties of [MMim]2[CuI3] crystals were both experimentally measured and theoretically calculated. These crystals exhibit intense broadband orange luminescence with pronounced Stokes shifts and a microsecond-scale fluorescence lifetime decay, primarily due to self-trapped exciton emission. Temperature-dependent fluorescence spectra were also recorded to explore the luminescence mechanism. In summary, these findings highlight the remarkable potential of lead-free [MMim]2[CuI3] crystals in advancing optoelectronic applications.