Synthesis and Upconversion Luminescence of High-Quality Water-Soluble NaYF4:Yb3+,Er3+ Nanoclusters

Hexagonal phase NaYF4:Yb3+,Er3+ nanoclusters were prepared using a facile solvothermal method. The structures and morphologies of the products were investigated using an X-ray powder diffractometer and a transmission electron microscope. Modified by the capping agent of poly(acrylic acid), the as-prepared NaYF4 NCs show excellent water solubility. Under 980-nm excitation, the aqueous solution of the sample displayed a bright green upconversion (UC) fluorescence. The luminescence dynamics were further studied based on the UC excitation pathways and the emission processes. Such water soluble UC samples may find application in the field of biological imaging.