Cation Occupation Engineering Realizes Valence Modulation of Manganese-Activated ZnGa₂O₄

Herein, a series of Mn-activated ZnGa₂O₄ (ZGO) phosphors have been developed for multifunctional applications. The characteristic green and red emission at 503 and 668 nm of Mn-activated ZGO phosphors can be observed under excitation of 247 and 375 nm, respectively, attributed to the partial oxidation of Mn²⁺ ions resulting in the coexistence of Mn²⁺ and Mn⁴⁺ ions in the host lattice. The valence modulation of Mn content not only realizes the adjustment of red and green luminescence intensity but also achieves the management of persistent luminescence time and thermo-luminescence time. Further, the codoping of Mg²⁺ could transform the position occupancy preference of Mn and effectively facilitate the conversion of Mn²⁺ to Mn⁴⁺, leading to the regulation of the valence state of manganese ions. Surprisingly, the existence of Mg²⁺ ions broadens the emission band of Mn⁴⁺ and enhances the photoluminescence intensity to 3.8 times, which can be ascribed to the weakened crystal field leading to the downward shift of the ⁴T₂ energy level and the increase of Mn⁴⁺ concentration. For this valence modulation behavior, two different hypotheses about the occupancy of Mg²⁺ have been proposed to explain the corresponding phenomenon. Finally, the potential applications of the synthesized phosphors have been explored in advanced anticounterfeiting strategies, information storage, and plant lighting field.