Photophysical studies for Cu(i)-based halides: broad excitation bands and highly efficient single-component warm white-light-emitting diodes

Designing and synthesizing cuprous halide phosphors unifying efficient low-energy emission and a broad excitation band is still a great challenge. Herein, by rational component design, three novel Cu(i)-based metal halides, DPCu₄X₆ [DP = (C₆H₁₀N₂)₄(H₂PO₂)₆; X = Cl, Br, I], were synthesized by reacting p-phenylenediamine with cuprous halide (CuX), and they show similar structures, consisting of isolated [Cu₄X₆]^2- units separated by organic layers. Photophysical studies uncover that the highly localized excitons and rigid environment give rise to highly efficient yellow-orange photoluminescence in all compounds with the excitation band spanning from 240 to 450 nm. The bright PL in DPCu₄X₆ (X = Cl, Br) originates from self-trapped excitons due to the strong electron-phonon coupling. Intriguingly, DPCu₄I₆ features a dual-band emissive characteristic, attributed to the synergistic effect of halide/metal-to-ligand charge-transfer (X/MLCT) and triplet cluster-centered (³CC) excited states. Benefiting from the broadband excitation, a high-performance white-light emitting diode (WLED) with a high color rendering index of 85.1 was achieved using single-component DPCu₄I₆ phosphor. This work not only unveils the role of halogens in the photophysical processes of cuprous halides, but also provides new design principles for high-performance single-component WLEDs.