Surface Modification of Upconversion Nanophosphors with Poly(acrylic acid)

Abstract

The upconversion bioimaging using infrared excitation is expected to solve the problems caused by an ultraviolet or visible excitation light, which damages the organic items in the system and limits the observation time in the conventional fluorescence bioimaging. Yttrium oxide particle doped with erbium are known to show the upconversion and be useful for the upconversion bioimaging. In this study, poly(acrylic acid) (sodium salt) (PAAcNa) was used for both the precursor preparation before calsination and the surface-modification of yttrium oxide nanophosphors doped with 2 mol% of erbium after the calcination. It was found that the use of PAAcNa resulted in a small particle size of 33 nm. The surface modification with PAAcNa increased the dispersion stability and chemical durability of the nanophoshpors in aqueous solution with the pH = 5-10.