Improving the luminescence and afterglow properties of Mg3Y2Ge3O12:Cr3+ by co-doping Bi3+

Generally, the emission intensity and afterglow of the near infrared phosphors can be improved by co-doping the sensitizer. In this work, Bi3+ ions as sensitizer are introduced into the near infrared phosphor Mg3Y2Ge3O12:Cr3+, and the luminescence properties are investigated. According to the principle of radius adaptation, Bi3+ ions would occupy eight coordinates in the host instead of Y3+ and Mg2+. Through structural refinement, theoretical calculation and experimental phenomena, there are two kinds of luminescent sources for Bi3+ ions, which come from 3P1 → 1S0 (441 nm) and MMCT (330 nm), respectively. In addition, the substitution of Bi3+ for Mg2+ will result in inequivalent substitution forming defects (BiMg·), and the trap depth is 0.55 eV. For Bi3+ and Cr3+ co-doped Mg3Y2Ge3O12, there are two factors can that can affect the luminescent properties of Cr, which are energy transfer and defects. The samples are obtained with three times the original emission intensity with the introduction of defects. At the same time, Bi3+ ions capture electrons to form new electron traps Bi2+ (Bi3+ + e-) and the trap depth is 0.81 eV. Therefore, under the action of two traps BiMg· and Bi2+ (Bi3+ + e-), the afterglow characteristics of the samples are improved and the time can reach 1.5 h.