Photonic Energy Back Transfer for Enhanced Upconversion/NIR-II Luminescence with 3D-Printed Manufacturing for Bone Imaging.

In this study, cubic-phase YOF is first identified as a suitable luminescent host for rare earth nanoparticle (RENP) through molecular dynamics simulations. By optimizing the core-shell structure, doping elements, and their ratios in the nanoparticles, the enhancement effect of energy back transfer (EBT) from Nd³⁺ to Er³⁺ on Nd³⁺ near-infrared-II (NIR-II) luminescence and Er³⁺ upconversion luminescence (UCL) is discovered. By separating the emission elements of NIR-II luminescence and UCL, energy competition is avoided, enabling the simultaneous enhancement of NIR-II luminescence and two-photon UCL. Based on this optimized NIR-II emission, high-quality in vivo vascular and bone imaging in mice are achieved. Finally, the potential of this optimized RENP as a novel bone material is explored using 3D printing technology. The proposed SiO₂-RENP multilayer structure effectively prevents laser-induced ejection of pure RENP while enhancing biocompatibility and mechanical properties. Through in vivo implantation experiments, this multilayer material demonstrates excellent long-term stability and biocompatibility in the NIR-II window, indicating its great potential as a novel bone material.