Site‐Selective Occupation of Mn ²⁺ Activators for Tunable Luminescence in Well‐Designed CaZnGe ₂ O ₆ Phosphors

Abstract Crystal‐site engineering is an efficient strategy for tuning the luminescent properties of multicolor inorganic luminescent materials. However, the control of crystallographic site occupancy by a single activator ion in a unitary host lattice to obtain regulable multicolor output remains a formidable challenge. Herein, the strategy to manipulate site‐selective occupation of Mn 2+ activators by exploiting the self‐reduction behavior of Mn ions within the CaZnGe 2 O 6 host matrix is reported to obtain a versatile color output. The choice of manganese precursor (MnO 2 and MnCO 3 ) dictates the local coordination geometry, producing disparate dominant emission: dodecahedral [MnO 8 ] for green luminescence and octahedral [MnO 6 ] crystallographic sites for red emission. Additionally, the introduction of rare‐earth Ln 3+ (Ln = Sm, La, Gd, Tb) co‐dopants modifies the Mn 2+ distribution among available crystallographic sites, facilitating continuous emission color modulation from green to red. The synergistic effect facilitates tunable emission alongside a significantly enhanced photoluminescence quantum yield of 76.58% and prolonged afterglow duration. Practical demonstrations of co‐doped phosphors confirm outstanding performance in anti‐counterfeiting, LED devices, and X‐ray detection applications. This work establishes a novel approach for color regulation in phosphors and provides valuable insights for designing multicolor multifunctional luminescent materials.