Functional Near Infrared-Emitting Cr³⁺/Pr³⁺ Co-Doped Zinc Gallogermanate Persistent Luminescent Nanoparticles with Superlong Afterglow for <i>in Vivo</i> Targeted Bioimaging

Near infrared (NIR)-emitting persistent luminescent nanoparticles (PLNPs) have great potential for <i>in vivo</i> bioimaging with the advantages of no need for <i>in situ</i> excitation, high signal-to-noise ratio, and deep tissue penetration. However, functional NIR-emitting PLNPs with long afterglow for long-term <i>in vivo</i> imaging are lacking. Here, we show the synthesis of NIR-emitting long-persistent luminescent nanoparticles (LPLNPs) Zn_2.94Ga_1.96Ge₂O₁₀:Cr³⁺,Pr³⁺ by a citrate sol–gel method in combination with a subsequent reducing atmosphere-free calcination. The persistent luminescence of the LPLNPs is significantly improved via codoping Pr³⁺/Cr³⁺ and creating suitable Zn deficiency in zinc gallogermanate. The LPLNP powder exhibits bright NIR luminescence in the biological transparency window with a superlong afterglow time of over 15 days. A persistent energy transfer between host and Cr³⁺ ion in the LPLNPs is observed and its mechanism is discussed. PEGylation greatly improves the biocompatibility and water solubility of the LPLNPs. Further bioconjugation with c­(RGDyK) peptide makes the LPLNPs promising for long-term <i>in vivo</i> targeted tumor imaging with low toxicity