Single-phase white-light emission via mixed-valence Eu²⁺/Eu³⁺ and Tb³⁺ co-doping in lead-free vacancy-ordered perovskite Cs₂ZrCl₆

All-inorganic, lead-free halide perovskites are compelling for optoelectronics, yet room-temperature, low-cost, and scalable syntheses remain challenging. We report a rapid, solution-based route to vacancy-ordered Cs₂ZrCl₆ with Tb³⁺ and mixed-valence Eu²⁺/Eu³⁺ doping, enabled by H₃PO₂-assisted Eu(III)→Eu(II) reduction. The undoped host exhibits a broad self-trapped-exciton band (~400–600 nm). Tb³⁺ introduces sharp ⁵D₄→⁷F_J lines (green) with structured PLE near ~354/377 nm, evidencing host→Tb transfer. Eu³⁺ yields red ⁵D₀→⁷F_J emission (CT ~328 nm), while controlled Eu²⁺ formation adds a broadband 450–750 nm component. Together these centers produce tricolor, excitation-dependent luminescence. In a representative co-doped composition (Cs₂ZrCl₆:10%Tb,5%Eu), excitation at ~355 nm efficiently addresses Tb³⁺ and Eu centers concurrently, minimizing defect contributions and providing near-UV (≈350–380 nm) drive guidelines. These results deliver a room-temperature, scalable synthesis and a spectroscopic framework for Pb-free chromaticity control, supporting the development of energy-efficient, single-phosphor white emitters.