Upconversion Luminescence and Temperature Sensing Properties of Er3+/Yb3+-Doped α-BiNbO4 Phosphor

Nowadays, optical thermometry has attracted considerable attention because of its non-contact feature, high spatial resolution and fast response. In this work, Er 3+ /Yb 3+ -doped orthorhombic-phase BiNbO 4 ( α -BiNbO 4 :Er 3+ /Yb 3+ ) phosphors are synthesized using the solid-state method to investigate the application of the material as an optical temperature sensor. X-ray diffraction (XRD) results reveal that all synthesized samples present a single orthorhombic phase, and Er 3+ /Yb 3+ ion doping does not change the crystal structure. Under 980-nm laser excitation, two green emission bands located at 534 nm ( 2 H 11/2 → 4 I 15/2 ) and 558 nm ( 4 S 3/2 → 4 I 15/2 ) and one red emission band centered at 672 nm ( 4 F 9/2 → 4 I 15/2 ) are observed. The doping concentration has a significant effect on the fluorescence properties of the phosphors, and the optimal doping concentrations in the α -BiNbO 4 host material are 3 mol.% Er 3+ and 15 mol% Yb 3+ . The temperature-dependent upconversion emission spectra are investigated in the range of 150–500 K. The performance of the material as an optical temperature sensor is investigated based on the fluorescence intensity ratio (FIR) technique. Its maximum values of absolute sensitivity ( S a ) and relative sensitivity ( S r ) are 5.51‰ K −1 at T = 415 K and 3.7% K −1 at T = 150 K, respectively. Finally, its repeatability and the laser heating effect are discussed. The results show that α -BiNbO 4 :Er 3+ /Yb 3+ phosphors have potential for application in non-contact optical temperature sensors.