Enhanced red emission from GdF₃:Yb³⁺,Er³⁺ upconversion nanocrystals by Li⁺ doping and their application for bioimaging

Under 980 nm near-infrared (NIR) excitation, upconversion luminescent (UCL) emission of GdF₃:Yb,Er upconversion nanoparticles (UCNPs) synthesized by a simple and green hydrothermal process can be tuned from yellow to red by varying the concentration of dopant Li⁺ ions. A possible mechanism for enhanced red upconverted radiation is proposed. A layer of silica was coated onto the surface of GdF₃:Yb,Er,Li UCNPs to improve their biocompatibility. The silica-coated GdF₃:Yb,Er,Li UCNPs show great advantages in cell labeling and in vivo optical imaging. Moreover, GdF ₃ UCNPs also exhibited a positive contrast effect in T ₁-weighted magnetic resonance imaging (MRI). These results suggest that the GdF₃ UCNPs could act as dual-modality biolabels for optical imaging and MRI. Dual-modality biolabels: GdF₃:Yb,Er upconversion nanoparticles (UCNPs) can be tuned in emission color from yellow to increasingly red by doping with Li⁺ ions (see figure). The red emission of silica-coated GdF₃:Yb,Er,Li UCNPs has great potential for in vivo and in vitro optical imaging, while the positive-contrast effect of their Gd ³⁺ ions allows them to be used in magnetic resonance imaging.