Photoluminescence and Radiation Luminescence in a Hybrid Cuprous (I) Halide: (4,4‐Difluoro‐bipiperidinium)3Cu2I5

Abstract Copper (I) based halide scintillators have received high attention due to their high light yield. At the same time, researchers are increasingly interested in exploring organic‐inorganic hybrid copper(I) based halides, due to the diversity and tunability of structures. Here, we describe high‐efficiency photoluminescence and X‐ray excited luminescence in (DFPD) 3 Cu 2 I 5 ( 1 ) (DFPD=4,4‐difluoro‐bipiperidinium). 1 is comprised of a unique [Cu 2 I 5 ] 3− cluster, which have typical structure allowing high‐transition‐probability self‐trapped exciton emission (one Cu + ion adopts the tetrahedral coordination geometry, the other trigonal planar coordination geometry, the Cu−Cu distance (2.574 Å) is short). Accordingly, 1 shows efficient yellow‐green photoluminescence with the maximum at 527 nm, a full‐width at half‐maximum of 99.2 nm, a large Stokes shift of 214 nm (1.6 eV) and a quantum yield of 77.15 %. Polycrystalline 1 can also convert high‐energy X‐ray photons into UV‐visible pulsed fluorescence with the light yield of 5000 photons/MeV. This finding plays a valuable role in the development of organic‐inorganic hybrid copper(I) based scintillators.