Toward Rechargeable Persistent Luminescence for the First and Third Biological Windows via Persistent Energy Transfer and Electron Trap Redistribution

Persistent luminescence (PersL) imaging without real-time external excitation has been regarded as the next generation of autofluorescence-free optical imaging technology. However, to achieve improved imaging resolution and deep tissue penetration, developing new near-infrared (NIR) persistent phosphors with intense and long duration PersL over 1000 nm is still a challenging but urgent task in this field. Herein, making use of the persistent energy transfer process from Cr3+ to Er3+, we report a novel garnet persistent phosphor of Y3Al2Ga3O12 codoped with Er3+ and Cr3+ (YAGG:Er-Cr), which shows intense Cr3+ PersL (similar to 690 nm) in the deep red region matching well with the first biological window (NIR-I, 650-950 nm) and Er3+ PersL (similar to 1532 nm) in the NIR region matching well with the third biological window (NIR-III, 1500-1800 nm). The optical imaging through raw-pork tissues (thickness of 1 cm) suggests that the emission band of Er3+ can achieve higher spatial resolution and more accurate signal location than that of Cr3+ due to the reduced light scattering at longer wavelengths. Furthermore, by utilizing two independent electron traps with two different trap depths in YAGG:Er-Cr, the Cr3+/Er3+ PersL can even be recharged in situ by photostimulation with 660 nm LED thanks to the redistribution of trapped electrons from the deep trap to the shallow one. Our results serve as a guide in developing promising NIR (>1000 nm) persistent phosphors for long-term optical imaging.