Ultralong near-infrared persistent luminescence in a Cr3+-doped gallogermanate for multifunctional applications

Near-infrared (NIR) persistent luminescence (PersL) materials show promising prospects in achieving multifunctional applications. However, the lack of excellent NIR PersL materials with high PersL brightness and ultralong PersL duration hinders their practical applications. Herein, we report a Cr3+-doped broadband NIR phosphor Mg8.9Ga14.2Ge4.9O40:Cr3+ (MGGO:Cr3+) with tunable photoluminescence and excellent PersL performance. The NIR emission wavelength of MGGO:Cr3+ can be tuned from 692 to 865 nm due to the multi-site occupation of Cr3+ ion. The designed MGGO:0.05Cr3+ phosphor exhibits intense NIR PersL in the wavelength range of 600-1100 nm with a PersL duration longer than 55 h. The ultralong PersL characteristic mainly originates from the slow release of electrons from deep traps. Through detailed analysis of trap energy levels and electron charging/de-trapping process, a possible PersL mechanism of MGGO:Cr3+ is proposed. Finally, we demonstrate the potential applications of MGGO:Cr3+ in broadband NIR phosphor-converted light-emitting diode devices, tissue penetration, labelling and tracing, multi-level anti-counterfeiting and encryption fields.