Engineering of Rare-Earth-Metal Oxysulfate (RE2O2SO4) Hollow Nanospheres for Upconversion

Bulk glass and crystalline materials are usually used for upconversion, but bulk materials are often not suitable for certain applications such as biological imaging or biolabelling. Upconversion materials on nanometer scales are desirable. However, synthesis of small nanocrystals that exhibit high monodispersibility and excellent upconversion properties remains a challenge.

In this work, nanoscale monodisperse rare-earth-metal-doped oxysulfate RE₂O₂SO₄ (RE = Y, Gd) hollow spheres were prepared for upconversion via a biomolecule-assisted hydrothermal method followed by calcination. The size and crystallinity of nanospheres, as well as the upconversion properties could be tuned by changing the experimental conditions such as surfactants, hydrothermal/annealing temperature, and chemical compositions. Upconversion properties revealed that the energy transfer between the sensitizer and the activator was strongly depended on the concentration of activator, the ratio of sensitizer to activator, chemical compositions and crystallinity of the hollow spheres.