Mg doping induced enhancement of persistent luminescence of ZGGO: Cr3+ nanoparticles for time-gate optical encryption

Herein, ZMGGO:Cr 3+ nanoparticles were prepared by incorporating Mg 2+ ions into Cr 3+ -doped zinc gallogermenate nanoparticles through a hydrothermal path in combination with a vacuum heating. The average size of ZMGGO:Cr 3+ nanoparticles minishes from 59 to 12 nm with growing Mg 2+ concentration. Meanwhile their luminescence intensity at 696 nm of ZMGGO:Cr 3+ nanoparticles was only decreased by less than half of that of the undoped nanoparticles due to the decreased particle size after Mg doping. Meanwhile, the integral luminescence intensity of their entire emission band shows an increasing trend with increasing temperature due to the enhanced phonon sideband luminescence at high temperature. More important, it is found that the formation energies associated with Mg′ Ga -Ga o Zn and Zn′ Ga -Ga o Zn defects are −1.2 and 1.69 eV, respectively, suggesting the enhanced afterglow intensity of ZMGGO:Cr 3+ can be ascribed to Mg doping leading to the increased number of these anti-site traps. Finally, the dual-level time-gate optical encryption was demonstrated using phosphorescent inks containing ZMGGO:Cr 3+ nanoparticles with different afterglow intensities.