One pot synthesis and optimized luminescent intensity of Gd2(WO4)3: Yb3+/Ho3+@SiO2 nanoparticles for biological application

The upconversion nanoparticles (UCNPs) have been widely used to biological field based on their outstanding advantages. In particular, fluorides are paid more attention while there is less focus on oxides. In fact, rare earth ion doped oxides possess excellent optical properties, which also can be regard as candidates for bioimaging, drug delivery, photodynamic therapy (PDT), photothermal therapy (PTT) and so on. In this work, the SiO2 coated Gd-2(WO4)(3): Yb3+/Ho3+ nanoparticles are synthetized by one pot co-precipitation method. The UCNPs exhibit strong green (526-560 nm) and red (628-677 nm) emissions under the 980 nm laser irradiation. And the luminescence intensity of UCNPs can be affected strongly by the thickness of SiO2, the thicker or thinner shell will be not conducive to the enhancement of fluorescence intensity. Furthermore, the optimal doping concentration is obtained by the evolution of luminescence intensity with different Yb3+/Ho3+ concentrations. The in vitro experiment result suggests that the tumor and normal cells have high viability after incubated with UCNPs even at high concentration, indicating the Gd-2(WO4)(3): Yb3+/Ho3+@SiO2 UCNPs have potential applications in biological field.