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

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.