Incorporation of Mg2+/Si4+ in ZnGa2O4:Cr3+ to Generate Remarkably Improved Near-Infrared Persistent Luminescence

Near-infrared emitting nano-sized particles of ZnGa2−x(Mg/Si)xO4:Cr3+ (x = 0–0.15, termed as ZGMSO:Cr3+) with persistent luminescence were prepared by sol-gel processing followed by calcination. The samples were tested by XRD, TEM, STEM, SAED, Raman, XPS, UV-Vis-NIR, TL, PLE/PL spectroscopy, and persistent luminescence decay analysis. Equimolar incorporation of Mg2+ and Si4+ ions did not change the spindle structure of ZnGa2O4 seriously. Most Mg2+ ions are more likely to occupy the sites in octahedron, but Si4+ ions are more likely to occupy the sites in tetrahedron in priority. A broader bandgap, up shift of conduction band minimum, and more anti-defects were found at a higher Mg2+/Si4+ doping concentration. ZGMSO:Cr3+ outputs near-infrared emission with a dominated band at 694 nm (2E → 4A2 transition of Cr3+), which can last longer than 48 h after the stoppage of UV irradiation. Mg2+/Si4+ doping contributes to a better near-infrared persistent luminescence, and the strongest and the longest NIR afterglow was observed at x = 0.05, owing to that the x = 0.05 sample has the deepest defects. The synthesized nanoparticles of ZGMSO:Cr3+ not only output intense NIR afterglow but also can be recharged by the red light of LED several times, indicating that they are the potential nano probes for bio imaging in living animals.