Lanthanide ion doped GdVO4 upconversion nanoparticles (UCNPs) have been synthesized via a simple hydrothermal process assisted with polyvinylpyrrolidone (PVP). The PVP had great effects on the morphology and luminescent intensity of the final products. Multicolor upconversion emissions such as orange, yellow, green and blue light can be generated by simply changing the codopant compositions or concentrations in these nanoparticles. A thin layer of silica was coated onto the surface of GdVO4 UCNPs to form a core/shell structure in order to improve their biocompatibility. The applications of the low-toxicity, silica-coated GdVO4 UCNPs as bio-tag for cell labeling and in vivo animal imaging were reported. In addition, the GdVO4 nanoparticles showed high contrast T1-enhancing modality due to the presence of Gd3+ ions on the particle surface. Hence, this newly developed multicolor GdVO4 UCNPs, which can be added into the upconversion nanomaterials family, could be used as a promising nanoprobe for dual-modality with optical bioimaging and magnetic resonance imaging (MRI).
