Achieving Narrowed Bandgaps and Blue‐Light Excitability in Zero‐Dimensional Hybrid Metal Halide Phosphors via Introducing Cation–Cation Bonding

Zero‐dimensional (0D) hybrid metal halides, which consist of organic cations and isolated inorganic metal halide anions, have emerged as phosphors with efficient broadband emissions. However, these materials generally have too wide bandgaps and thus cannot be excited by blue light, which hinders their applications for efficient white light‐emitting diodes (WLEDs). The key to achieving a blue‐light‐excitable 0D hybrid metal halide phosphor is to reduce the fundamental bandgap by rational chemical design. In this work, we report two designed hybrid copper(I) iodides, (Ph 3 MeP) 2 Cu 4 I 6 and (Cy 3 MeP) 2 Cu 4 I 6 , as blue‐light‐excitable yellow phosphors with ultrabroadband emission. In these compounds, the [Cu 4 I 6 ] 2− anion forms an I 6 octahedron centered on a cationic Cu 4 tetrahedron. The strong cation–cation bonding within the unique cationic Cu 4 tetrahedra enables significantly lowered conduction band minimums and thus narrowed bandgaps, as compared to other reported hybrid copper(I) iodides. The ultrabroadband emission is attributed to the coexistence of free and self‐trapped excitons. The WLED using the [Cu 4 I 6 ] 2− anion‐based single phosphor shows warm white light emission, with a high luminous efficiency of 65 lm W −1 and a high color rendering index of 88. This work provides strategies to design narrow‐bandgap 0D hybrid metal halides and presents two first examples of blue‐light‐excitable 0D hybrid metal halide phosphors for efficient WLEDs.