Regulating anti-site defects in MgGa2O4:Mn4+ through Mg2+/Ge4+ doping to greatly enhance broadband red emission for plant cultivation

Non-rare-earth Mn4+-activated broadband emission deep-red phosphors are considered as the potential red emitter in indoor plant growth LEDs owing to that their emission peaks can well overlap with the absorption of plant pigments. Here, a series of Mg2+xGa4−2xGexO8:0.001Mn4+ (MGGO:0.001Mn4+) phosphors were synthesized by a traditional high-temperature solid-state reaction. Incorporation of Mg2+/Ge4+ resulted in decreased Mg/Ga anti-site at x = 0–0.5 and increased Mg/Ga anti-site at x = 0.5–0.7, which contributed to the expanded and the contractive lattice constant, respectively. Because Mn4+ ions occupy two kinds of octahedral sites, that are the sites near to [MgO6] and [GaO6] respectively, the phosphor exhibited asymmetric broadband emission from 600 to 800 nm with the maximum at 677 nm (4T2 → 4A2 transition of Mn4+). Besides, doping Mg2+/Ge4+ in MgGa2O4 significantly affects the symmetry of octahedra and thus yields an enhancement of the broadband emission for Mn4+ by 1.6 times. Moreover, the emission spectra of phosphors overlap well with the absorption spectra of plant pigments, indicating that MGGO:0.001Mn4+ phosphors have an application prospect for plant cultivation.