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, Er3+/Yb3+-doped orthorhombic-phase BiNbO4 (alpha-BiNbO4:Er3+/Yb3+) 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 Er3+/Yb3+ ion doping does not change the crystal structure. Under 980-nm laser excitation, two green emission bands located at 534 nm (H-2(11/2) -> I-4(15/2)) and 558 nm (S-4(3/2) -> I-4(15/2)) and one red emission band centered at 672 nm (F-4(9/2) -> I-4(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 alpha-BiNbO4 host material are 3 mol.% Er3+ and 15 mol% Yb3+. 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 parts per thousand 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 alpha-BiNbO4:Er3+/Yb3+ phosphors have potential for application in non-contact optical temperature sensors.

Automated summary

In this study, Er3+/Yb3+-doped orthorhombic-phase BiNbO4 phosphors were synthesized and investigated as optical temperature sensors. The optimal doping concentrations were determined to be 3 mol.% Er3+ and 15 mol.% Yb3+. The material showed maximum absolute sensitivity (S-a) of 5.51‰/K at 415 K and relative sensitivity (S-r) of 3.7%/K at 150 K using the fluorescence intensity ratio technique.