Near Ultraviolet‐Excitable Cyan‐Emissive Hybrid Copper(I) Halides Nonlinear Optical Crystals with Near‐Unity Photoluminescence Quantum Yield and High‐Efficiency X‐ray Scintillation

Designing and synthesizing multifunctional hybrid copper halides with near ultraviolet (NUV) light-excited high-energy emission (<500 nm) remains challenging. Here, a pair of broadband-excited high-energy emitting isomers, namely, α-/β-(MePh₃P)₂CuI₃ (MePh₃P=methyltriphenylphosphonium), were synthesized. α-(MePh₃P)₂CuI₃ with blue emission peaking at 475 nm is firstly discovered wherein its structure contains regular [CuI₃]^2- triangles and crystallizes in centrosymmetric space group P2₁/c. While β-(MePh₃P)₂CuI₃ featuring distorted [CuI₃]^2- planar triangles shows inversion symmetry breaking and crystallizes in the noncentrosymmetric space group P2₁, which exhibits cyan emission peaking at 495 nm with prominent near-unity photoluminescence quantum yield and the excitation band ranging from 200 to 450 nm. Intriguingly, β-(MePh₃P)₂CuI₃ exhibits phase-matchable second-harmonic generation response of 0.54×KDP and a suitable birefringence of 0.06@1064 nm. Furthermore, β-(MePh₃P)₂CuI₃ also can be excited by X-ray radioluminescence with a high scintillation light yield of 16193 photon/MeV and an ultra-low detection limit of 47.97 nGy/s, which is only 0.87 % of the standard medical diagnosis (5.5 μGy/s). This work not only promotes the development of solid-state lighting, laser frequency conversion and X-ray imaging, but also provides a reference for constructing multifunctional hybrid metal halides.