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

Abstract 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‐ (MePh 3 P) 2 CuI 3 (MePh 3 P=methyltriphenylphosphonium), were synthesized. α‐ (MePh 3 P) 2 CuI 3 with blue emission peaking at 475 nm is firstly discovered wherein its structure contains regular [CuI 3 ] 2− triangles and crystallizes in centrosymmetric space group P 2 1 / c . While β ‐(MePh 3 P) 2 CuI 3 featuring distorted [CuI 3 ] 2− planar triangles shows inversion symmetry breaking and crystallizes in the noncentrosymmetric space group P 2 1 , 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 ‐(MePh 3 P) 2 CuI 3 exhibits phase‐matchable second‐harmonic generation response of 0.54×KDP and a suitable birefringence of 0.06@1064 nm. Furthermore, β ‐(MePh 3 P) 2 CuI 3 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 μ Gy/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.