Red to near infrared ultralong lasting luminescence from Mn2+-doped sodium gallium aluminum germanate glasses and (Al,Ga)-albite glass-ceramics
For specific techniques of bioimaging or photodynamic tumor therapy, it is highly desirable to find a luminescent material with emission wavelengths within the region of transparency of biological tissue, i.e., 650 – 1300 nm, and with multiple-hour luminescence afterglow. Here, we demonstrate red to near-infrared persistent luminescence from Mn2+ doped sodium gallium aluminum germanate glasses, covering the spectral region of 600 to 800 nm. Persistent luminescence from octahedral Mn2+ is associated with the presence of electronic defects with depths of 0.71 eV, 0.80 eV and 1.06 eV, which de-trap thermally at ambient temperature. The process of de-trapping occurs over a time of more than 40 h. When nanocrystalline high-albite Na(Al,Ga)Ge3O8 is precipitated from the supercooled melt through controlled thermal annealing, the red afterglow can be preserved, and the afterglow duration can be further extended to more than 100 h. This originates from the incorporation of Mn2+ on octahedral lattice sites with a more ionic bonding character in the compound, and a significant increase of defect density with, at the same time, decreasing depth, i.e., 0.70 eV, 0.75 eV and 0.85 eV. The observed properties suggest that the Mn2+ doped Na(Al,Ga)Ge3O8 nanocrystal may provide a new solution to in vivo bioimaging or photodynamic tumor therapy.