One-step synthesis of NaLu80−xGdxF4:Yb183+/Er23+(Tm3+) upconversion nanoparticles for in vitro cell imaging

Upconversion nanoparticles (UCNPs) possess a unique type of photoluminescence (PL) in which lower-energy excitation is converted into higher-energy emission via multi-photon absorption processes. In this work, we have used a facile one-step hydrothermal method promoted water solubility to synthesis NaLuGdF4:Yb3 +/Er3 +(Tm3 +) UCNPs coated with malonic acid (MA). Scanning electron microscopy images and X-ray diffraction patterns reveal sphere-shaped UCNPs with an average size of ~ 80 nm crystallized in the cubic NaLuF4 structure. The characteristic vibrations of cubic UCNPs have been taken into account by using Fourier-transform infrared spectroscopy. Based on PL studies, we have determined an optimal concentration of Gd3 + doping. The dependence of upconversion PL intensity on Gd3 + concentration is discussed via the results of magnetization measurements, which is related to the coupling/uncoupling of Gd3 + ions. Particularly, our study reveals that carboxyl-functionalized NaLuGdF4:Yb3 +/Er3 +(Tm3 +) UCNPs have a relatively high cell viability with HeLa cells.