Neutron‐Resolved Double Spinel Host Engineering for Ultra‐Broadband NIR Luminescence and Cr ³⁺ , Ni ²⁺ Energy Transfer

Abstract Broadband Cr ³⁺ ‐ and Ni ²⁺ ‐activated spinel phosphors have garnered significant attention for their potential in near‐infrared (NIR) applications. Yet, the role of local structure in governing their photoluminescence properties remains underexplored. Here, a series of Cr ³⁺ ‐ and Ni ²⁺ ‐doped Zn _{1‐ x} AlGa _{1+ x *2/3} O ₄ ( x = 0–0.4) phosphors have been designed, tuned via Zn‐deficiency to modulate cation inversion and local structural disorder. Through neutron total scattering with pair distribution function analysis, this work presents the first demonstration of a neutron‐based multiscale structure‐property relationship linking local cation disorder to NIR luminescence. Specifically, the optimized composition ( x = 0.3) exhibits a pronounced short‐range tetragonal cation ordering ( P4 ₁ 22 symmetry) coexisting within a well‐ordered long‐range Fd‐3m spinel framework. Mono‐doped phosphors show enhanced emission, with Cr ³⁺ emission radically broadened and Ni ²⁺ intensity enhanced fourfold due to inversion‐induced lattice distortion. Substantially, the Cr ³⁺ , Ni ²⁺ co‐doping in optimized Zn _0.7 AlGa _1.20 O ₄ ( x = 0.3) extends the NIR emission to an impressive 650–1600 nm and markedly boosts external quantum efficiency (EQE) of Ni ²⁺ emission from 3.6% to 46.9%. This study demonstrates the impact of novel host engineering on NIR luminescence properties, establishes neutron scattering as a strategic tool for probing emission mechanisms, and highlights the multifunctionality of highly‐efficient Zn _0.7 AlGa _1.20 O ₄ :Cr ³⁺ , Ni ²⁺ co‐doped phosphors.