Lead-based perovskites have received great attention due to their excellent optoelectronic characteristics, but the instability and intrinsic toxicity of lead are still critical issues for their practical applications. To overcome these drawbacks, exploring the nontoxic substitution of lead in perovskites while maintaining the outstanding behaviors of perovskites is significantly important. Recently, copper has been regarded as a promising candidate to replace lead due to its low environmental effect, abundance, and low cost. Copper-based halides tend to form highquality low-dimensional compounds with structural and compositional flexibility, and they have been used for fabricating optoelectronic devices, such as light-emitting diodes (LEDs), photodetectors, and X-ray scintillators.

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Lead-based perovskites have received great attention due to their excellent optoelectronic characteristics, but the instability and intrinsic toxicity of lead are still critical issues for their practical applications. To overcome these drawbacks, exploring the nontoxic substitution of lead in perovskites while maintaining the outstanding behaviors of perovskites is significantly important. Recently, copper has been regarded as a promising candidate to replace lead due to its low environmental effect, abundance, and low cost. Copper-based halides tend to form highquality low-dimensional compounds with structural and compositional flexibility, and they have been used for fabricating optoelectronic devices, such as light-emitting diodes (LEDs), photodetectors, and X-ray scintillators.

We synthesized all-inorganic ternary copper halides including spherical Cs₃Cu₂X₅ (X = Cl, Cl/Br, Br, Br/I, and I) nanocrystals with PL peaks ranging from 440 to 530 nm, CsCu₂I₃ nanocrystals with an emission peak of 575 nm, and deep-blue emissive A₂CuX₃ (A = K, Rb; X = Cl, Br) nano/microcrystals with controllable morphologies. Among them, green luminescent Cs₃Cu₂Cl₅ and deep-blue luminescent K₂CuCl₃ possess a remarkable high photoluminescence quantum yield (PLQY) value of ~100%. Moreover, with the incorporation of organic molecules into ternary copper halides, their structures can be further tuned to obtain more emission colors in the visible spectrum. Red-emissive A₆(DMSO)₁₂[Cu₈Br₁₃][Cu₄Br₄(OH)(H2O)] (ACB-DMSO, A = K, Rb; DMSO = dimethyl sulfoxide, C₂H₆OS) and A₆(C₄H₈OS)₁₂[Cu₈X₁₃][Cu₄X₄(OH)(H₂O)] (ACX-THTO, A = K, Rb, and Cs; X = Cl, Br) with deep-red to to near-infrared emissions were obtained. It was observed that the removal and addition of the solvent molecules resulted in the reversible transformation between the hybrid copper halides with 0D copper clusters and allinorganic copper compounds featuring one-dimensional (1D) chains. Furthermore, we conducted the liquid-liquid diffusion method to synthesize diverse categories of alkali copper(I) iodide (ACuI)-based (A = Na, K, Rb, and Cs) hybrid compounds with diverse structures. Their emission peaks are in the range of 530-660 nm, which can be tuned by the composition of alkali metals and organic molecules. The highest emission efficiency of 91% was achieved for KCuI₂(C₄H₈OS)₂ (658 nm), and yellow emissive Rb₂Cu₂I₄(C₄H₈OS)₃ showed excellent stability in the air. This solvent engineering is not only suitable for copper-based compounds, but it also works for sodium antimony bromides. Yellow emissive Na₃SbBr₆(C₂H₆OS)₆ and orange emissive Na₃SbBr₆(C₄H₈OS))₆ single crystals featuring 1D chains also can transform into each other. Additionally, we demonstrated their utilization as ink for inkjet printing or emitters for downconversion mono-color or white LEDs with excellent performance.