Dynamic and multimodal luminescence of Mn2+-doped Mg4Ga8Ge2O20 persistent phosphor for anti-counterfeiting applications†

The study provides an in-depth analysis of the structure and luminescence properties of Mg₄Ga₈Ge₂O₂₀:Mn²⁺ (MGGO) materials, focusing particularly on their dynamic color-changing capabilities. A series of single-phase MGGO:xMn²⁺ (0.0 ≤ x ≤ 0.5 mol%) was prepared. The successful incorporation of Mn²⁺ ions was verified using electron paramagnetic resonance spectroscopy. The photoluminescence and X-ray excited optical luminescence properties demonstrated that emission can be color-tuned based on the concentration of Mn²⁺ ions, with significant color shifts between red and blue observed during excitation and decaying of persistent luminescence. The persistent luminescence properties were characterized and analyzed, revealing complex decay behaviors that suggest a combination of tunneling and thermal detrapping mechanisms. Three types of traps were identified in the MGGO materials: shallow traps associated with intrinsic defect emission, deep traps, and Ga-related hole traps linked to Mn²⁺ emission. Notably, all MGGO samples can be characterized by red thermally stimulated luminescence, regardless of the initial luminescence color. These findings indicate that MGGO materials hold significant potential for anti-counterfeiting applications due to their dynamic and multimodal luminescent properties.