Red emission upconversion of NaYF4: Yb3+/Er3+ nanoparticles: Rapid preparation via single-mode focused microwave method and their application in cell imaging

The red emission of upconversion nanoparticles (UCNPs) is located in an "optical window" range of the biological tissue, which has a promising prospect in biology application. In this work, novel red-emitting NaYF4:Yb3+/Er3+ UCNPs with CH3COO− modifications were synthesized by single-mode focused microwave method. The morphology, structure, and luminescence properties of as-prepared UCNPs were characterized. The results showed that single-mode focused microwave method was an effective approach to prepare hydrophilic and strongly red emission UCNPs within a drastically reduced reaction time (only 10 min) compared to the traditional methods. Importantly, we also demonstrated that the CH3COO− modified NaYF4:Yb3+/Er3+ UCNPs could be successfully applied for in vitro imaging of HeLa cells. This work not only provides a rapidly synthetic methodology for the preparation of red-emitting UCNPs but also offers an effective material for cancer cell imaging.