One-step hydrothermal synthesis of carboxyl-functionalized upconversion phosphors for bioapplications.

Graphical One step at a time : Carboxyl-functionalized upconversion phosphors have been successfully synthesized with a facile one-step hydrothermal approach by using a small-molecule binary acid as capping agent (see figure). This is an environmental friendly and facile approach to the large-scale synthesis of carboxyl-functionalized upconversion materials with controlled phases, shapes, and sizes. In this paper, we report a facile one-step hydrothermal method to synthesize phase-, size-, and shape-controlled carboxyl-functionalized rare-earth fluorescence upconversion phosphors by using a small-molecule binary acid, such as malonic acid, oxalic acid, succinic acid, or tartaric acid as capping agent. The crystals, from nano- to microstructures with diverse shapes that include nanospheres, microrods, hexagonal prisms, microtubes, microdisks, polygonal columns, and hexagonal tablets, can be obtained with different reaction times, reaction temperatures, molar ratios of capping agent to sodium hydroxide, and by varying the binary acids. Fourier transform infrared, thermogravimetric analysis, and upconversion luminescence spectra measurements indicate that the synthesized NaYF 4 :Yb/Er products with hydrophilic carboxyl-functionalized surface offer efficient upconversion luminescent performance. Furthermore, the antibody/secondary antibody conjugation can be realized by the carboxyl-functionalized surfaces of the upconversion phosphors, thus indicating the potential bioapplications of these kinds of materials.