Efficient NIR to NIR up-conversion in LiYF4:Yb3+,Tm3+ micro-octahedrons by modified hydrothermal method

The efficient NIR-to-NIR upconverter of LiYF4:Yb3+,Tm3+ (simplified as LYF:Yb,Tm) was synthesized by a modified hydrothermal method in this work. The synthesized LYF:Yb,Tm has well controlled morphology of monodisperse micrometer sized octahedrons. XRD pattern confirms its pure tetragonal LiYF4 structure. The LYF:Yb,Tm exhibits a dominating NIR UC emission at ~793 nm along with relative weak blue and red UC emissions under 976 nm LD excitation. The optimal concentrations of Yb3+ and Tm3+ ions for NIR up-conversion (UC) emission are 20 mol% and 0.6 mol%, respectively. The internal UC quantum yield (IUCQY) of this LYF:Yb,Tm in NIR band is tested to be 5.1% at 959 nm LD excitation power density (PD) of 120 W/cm2. The UC emission mechanism is discussed based on UC fluorescent behaviors of Yb3+ and Tm3+. The results of fluorescent labeling indicate its potential applications in fluorescent markers, solar cells and 3D flat panel displays.