Trap distribution and mechanism for near infrared long-afterglow material AlMgGaO4:Cr3+

Near infrared (NIR) long-afterglow materials have attracted much attention due to their high penetration and low destruction in biological tissues. Here, a series of deep red and near infrared materials, AlMgGaO4:xCr3+, were successfully synthesized by a high temperature solid state method. AlMgGaO4 was selected as the host considering its rich antisite defects, which can effectively capture electrons. The emission spectra of AlMgGaO4:xCr3+ range from 680 nm to 1100 nm, which can be nicely decomposed into four Gaussian bands with peaks centered at 706 nm, 723 nm, 916 nm, and 938 nm, respectively. At low temperature (10 K), the emission spectra show there are four emission peaks: a sharp line (peak 1) and broad emission band (peak 2) come from Cr3+ substituting for the regular octahedron [AlO6], and two broad emission bands (peaks 3 and 4) which originate from the spin-allowed transition 4T2(4F) → 4A2(4F) of Cr3+ in the disordered [GaO6] and [MgO6] octahedra, respectively. Remarkably, after removing the excitation source, it exhibited more than 10 hours of afterglow emission which decreased sharply in the first 30 min and then decreased slowly. With an increase in the Cr3+ concentration, the trap depth became shallower due to the generation of the electronic trap centers . The distribution of trap centers and the mechanism of the persistent luminescence have been carefully analyzed and are also discussed.