Extremely intense green up-conversion luminescent and ultra-high temperature sensitivity in Er3+/Yb3+ co-doped BiTa7O19 phosphors

Er3+/Yb3+ co-doped BiTa7O19 phosphors with bright pure green emission were synthesized first by a solid-state reaction method. The lattice structure and morphology of the synthesized samples was determined by X-ray diffraction (XRD) and field emission scan electronic microscope (FESEM). These samples' up-conversion luminescence (UCL) and optical temperature sensing behavior were investigated by photoluminescence spectroscopy under 980 nm laser diode (LD) excitation. The optimum values of Er3+ and Yb3+ doping concentration were 10 mol % and 40 mol %, respectively. Further optimizing the preparation process of (Bi0.5Er0.1Yb0.4)Ta7O19, the green UCL integrated intensity of (Bi0.5Er0.1Yb0.4)Ta7O19 is up to 1.32 times than that of commercial NaYF4: Er3+/Yb3+ phosphors under 980 nm LD 35.71 W/cm(2) excitation. In addition, all Er3+/Yb3+ co-doped BiTa7O19 phosphors have a good green monochromaticity (S-gr), and the S-gr reached 0.98-0.99. Based on the fluorescence intensity ratio (FIR) of the transition emission of the thermally coupled H-2(11/2) and S-4(3/2) levels to the ground state, the maximum absolute sensitivity (S-A) of optimized (Bi0.5Er0.1Yb0.4)Ta7O19 is calculated as high as 0.01624 K-1 at 475 K, which is much higher than other reported materials. These results indicate that BiTa7O19: Er3+/Yb3+ may have potential applications in biological imaging, fluorescent labels, and optical temperature sensors.