Excitation-Dependent Emission in Zr4+-Doped Scandium-Based Zero-Dimensional Metal Halides for White Light-Emitting Diodes

All-inorganic zero-dimensional (0D) metal halides have emerged as promising candidates for lighting and anticounterfeiting applications due to their self-trapped exciton (STE) emission characteristics and relatively low toxicity. However, the effective modulation of single-phosphor emission remains a major challenge in the field of optical materials. Here, we unveil excitation-dependent emission modulation in 0D rare-earth metal halide Cs₂ScCl₅·H₂O microcrystals (MCs) via Zr⁴⁺ ion doping. Under 260 nm UV excitation, Zr⁴⁺-doped Cs₂ScCl₅·H₂O MCs exhibit intense blue emission with a remarkable photoluminescence quantum yield (PLQY) of 87%. Notably, excitation at 272 nm induces a pronounced red-shift in the emission, yielding bright neutral white light while maintaining a high PLQY of 85%. Spectroscopic and density functional theory (DFT) calculations reveal that the tunable emission properties of Zr⁴⁺-doped Cs₂ScCl₅·H₂O MCs arise from the coexistence of two distinct STE states. The high-energy blue emission is attributed to STE1 states, which are formed through strong electron-phonon coupling within the [ZrCl₅·H₂O]^- octahedron units. Furthermore, efficient energy transfers from Zr⁴⁺-associated STE1 states to the host-derived STE2 states enhance yellow emission. White light-emitting diodes (WLEDs) based on Zr⁴⁺-doped Cs₂ScCl₅·H₂O MCs are explored with color rendering index of 90.5 and color coordinate of (0.32, 0.33), which are very close to ideal white-light emission. This work proposes an innovative strategy for designing a novel 0D metal halide capable of achieving efficient single-component phosphor emission modulation.