Luminescent Properties and 3-Bit Ternary-Coding Optical Anti-Counterfeiting of Mg4Al4.5Ga2.45B1.05O16:Mn2 + /Mn4 +

A series of Mg4Al4.5Ga2.45B1.05O16:xMn (x = 0.01–0.06) phosphors were successfully synthesized via a high-temperature solid-state method. The crystal structure, luminescent properties, thermal stability, and anti-counterfeiting application was systematically investigated. Mn4+ undergoes self-reduction to form Mn2+ in air, resulting in emissions from both Mn2+ and Mn4+ present in the spinel matrix. Under excitation at 228 nm, the samples exhibit green emission at 514 nm (originating from Mn2+) whereas under excitation at 303 nm they show red emission at 662 nm (originating from Mn4+). Additionally, intermediate-color emission is obtained under coexcitation of Mn2+ and Mn4+ at 380 nm, enabling multicolor emission under three-wavelength excitation. From electron paramagnetic resonance and X-ray diffraction refinement, Mn2+ mainly occupies the tetrahedral Mg2+ sites, while Mn4+ occupies the octahedral Al3+/Ga3+ sites. The concentration quenching mechanism revealed that the quenching of Mn2+ and Mn4+ is dominated by adjacent-ion interaction and dipole–dipole interaction, respectively. Temperature-dependent spectral measurements show that the material possesses excellent thermal stability, with activation energies of 0.25 eV (for Mn2+) and 0.35 eV (for Mn4+), respectively. Benefiting from its multimodal luminescent characteristics, the material is suitable for 3-bit ternary coding optical anti-counterfeiting technology as a new anti-counterfeiting material.