Unusual Single Band 803 nm Persistent Luminescence of Tm-Doped Calcium Titanate Charged in the Near-Infrared Bio-Imaging Window

Lanthanide-doped materials were developed with interesting near-infrared (NIR) persistent luminescence (PersL) properties after X-ray irradiation but are limited by poor charging ability based upon biocompatible red light. In this study, CaTiO3:Tm (CTT) was found to emit an unusual single band PersL at ∼800 nm, which was rechargeable by red-NIR light excitation (∼650 to 720 nm). Moreover, blue or deep red light could charge more intense PersL than UV light in CTT, which was quite different from all the other known lanthanide-activated NIR PersL materials. An upconverting-energy transfer PersL mechanism was proposed based on the upconverting property of Tm3+ and its energy transfer to Ti3+ in the CaTiO3 matrix. The interaction of Tm3+ and Ti3+ in CaTiO3 quite possibly played an important role in the unusual PersL process of CTT, which avoided the band-pass transition of the CaTiO3 matrix. By comparison with a series of Tm-doped phosphors, CaTiO3 was found to be an optimal PersL matrix to generate the unique PersL properties of Tm3+. The in situ charged NIR PersL imaging of a medical stent implant in the neck of a chicken model was demonstrated. This study reveals the unusual PersL properties of CTT and will promote advanced biomedical applications of rare-earth-doped PersL biomaterials.