One-Dimensional Lead-Free Halide with Near-Unity Greenish-Yellow Light Emission

Low-dimensional metal halides (LDMHs), especially lead-based perovskites, have recently attracted a great deal of attention for their unique structures and optoelectronic properties. However, the toxicity of lead limits their practical applications. Herein, a lead-free one-dimensional copper-based halide KC22Cu4I6 (C = 12-crown-4 ether) was constructed, which exhibits greenish-yellow emission (545 nm) with a near-unity photoluminescence quantum yield (∼97.8%). To the best of our knowledge, this is the highest value that has been achieved in lead-free greenish-yellow light-emitting LDMHs. Density functional theory calculations combined with comprehensive spectroscopic data revealed the characteristics of self-trapped exciton emission. Finally, we explored the application of the KC22Cu4I6 phosphor by fabricating the white light-emitting diode (WLED) device. The WLEDs fabricated using commercially available blue (450 nm) and ultraviolet (365 nm) as the excitation source both present excellent luminescence properties with a high color rendering index and a suitable corresponding color temperature. Our findings not only expand the library of highly efficient luminescent materials but also highlight the potential of low-dimensional copper-based halides in optoelectronics.