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Manganese valence modulation in ZnGa2O4 via simultaneously localized charge accumulation and oxygen vacancy engineering controlled by Li+ and F- substitutions for tailored applications
C. X. Chen, W. Y. Li, C. Y. Ni, W. B. Dai*
https://doi.org/10.1016/j.cjsc.2026.100868
ZnGa2O4; Valence modulation; Mn; Lattice site engineering; Multimodal PL
ABSTRACT
Mn-activated phosphors have attracted great attention, but the inevitable self-reduction of Mn4+ to Mn2+ and precise regulation of Mn4+/Mn2+ content remain serious challenges. Herein, through solid-state reaction in air, we demonstrate that the degree of self-reduction and valence of Mn can be accurately manipulated in normal spinel ZnGa2O4 (ZGO) by incorporation of Li+ and F-, achieving color-tunable photoluminescence (PL) as desired, from blue self-luminescence to red/green emission of Mn4+/Mn2+. Both theoretical (i.e., density functional theory, bond energy theory) and experimental (i.e., dynamic/static spectroscopy) analyses indicate that Li+ occupying the tetrahedral Zn2+ site can push Mn4+ into the octahedral Ga3+ site and restrain self-reduction of Mn4+ owing to localized charge accumulation around Li+ that depletes excess electrons. Furthermore, F− substitution can repair intrinsic oxygen vacancies, further suppressing self-reduction and detrimental electron-capturing effects. Meanwhile, Li+/F− incorporation can distort ZGO and break the forbidden transition of Mn4+, leading to broadened PL and enhanced efficiency. The long-persistent PL (LPL) of ZGO: Mn/Li/F with wide shallow/deep traps is also explored in depth. Finally, the Li/F-dependent tunable PL and LPL of ZGO: Mn/Li/F show great potential for applications in ratiometric optical thermometers, plant lighting, white LEDs, and dynamic anticounterfeiting.
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