Organic–Inorganic Copper Halide Compound with a Near‐Unity Emission: Large‐Scale Synthesis and Diverse Light‐Emitting Applications

Abstract Low‐dimensional organic–inorganic metal halides (OIMHs) have emerged as promising light emitters due to their broadband emission originating from self‐trapped excitons (STE), especially for Cu‐based OIMHs. Herein, Cu(I)‐based OIMH with a structure of (TPP) 2 Cu 4 I 6 ·2DMSO (TPP stays for tetraphenylphosphonium, and DMSO – for dimethyl sulfoxide) has been synthesized, both in form of single crystals and as a microcrystalline powder. This compound exhibits a broadband green emission with a peak at 515 nm and a full width at half‐maximum of 78 nm, and a near‐unity photoluminescence quantum yield of 99.5%. Experimental data supported by theoretical calculations indicate that the STE emission is responsible for the green emission with a long lifetime of 2.53 µs. Down‐conversion light‐emitting device with a high luminous efficiency of 50 lm W −1 based on this compound have been fabricated, and white light has also been achieved with a high color rendering index of 96.7. Moreover, green emissive (TPP) 2 Cu 4 I 6 ·2DMSO is utilized in scintillators for X‐ray detection and imaging, and as a luminescent ink for encryption applications.