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, CaTiO: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 Tm and its energy transfer to Ti in the CaTiO matrix. The interaction of Tm and Ti in CaTiO quite possibly played an important role in the unusual PersL process of CTT, which avoided the band-pass transition of the CaTiO matrix. By comparison with a series of Tm-doped phosphors, CaTiO was found to be an optimal PersL matrix to generate the unique PersL properties of Tm. The 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.