Gd ₂ O ₃ Doped with Yb ³⁺ /Er ³⁺ for Boosted Downshifting Pathway in NIR-IIb Region and Exploring the Dynamics of MRI/NIR-II Imaging in the Nanophosphor

Lanthanide-ion-activated nanoparticles stimulated by 808 or 980 nm lasers present promising applications in biological imaging. This contribution reveals their physicochemical properties and explores their potential as near-infrared-II (NIR-II) fluorescent agents for bioimaging. Specifically, the NIR-IIb window (1500-1700 nm) has the advantages of low scattering and less autofluorescence from the tissues, which makes this region suitable for imaging with greater clarity. Lanthanides offer diverse emission possibilities due to their rich energy levels, which make them highly effective nanoprobes. This study focuses on gadolinium oxide (Gd₂O₃) as the host material due to its facile fabrication and low toxicity. The Gd₂O₃ system is doped with Yb³⁺ and Er³⁺ ions and achieves a high quantum efficiency of 22.8% in the NIR-IIx and NIR-IIb windows. Moreover, the superior penetrability of the NIR-IIb window is unveiled by the penetration depth testing and <i>in vivo</i> imaging studies. Additionally, Gd³⁺ ions exhibit magnetic properties, which support their application in magnetic resonance imaging (MRI). This work reveals the high brightness and high energy transfer efficiency of the Yb³⁺-Er³⁺ system and explores the feasibility of Gd₂O₃ nanoparticles in MRI. Therefore, we believe that this work provides a superior and biocompatible candidate for understanding the dynamics of MRI/NIR-II imaging of the nanophosphor for clinical applications.