Preparation and Upconversion Luminescence of β-NaYF4:Yb3+, Tm3+/ZnO Nanoparticles

β-NaYF4:Yb3+, Tm3+/ZnO core/shell nanoparticles (NPs) were synthesized via a high temperature thermal decomposition method. The as-synthesized core/shell NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and upconversion luminescence spectra (UCL). Under 980 nm laser excitation, the measured intensity of upconversion luminescence (1I6→3H6, 1I6→3F4, and 1D2→3H6) was different with and without ZnO. During the sample preparations, changing the ratio of the solvent affected the ZnO UV absorption efficiency. The results show that the NIR light can be used as the driving source to excite ZnO, thus extending utility rate to the NIR spectral region and enhancing the light harvest rate.