Up-conversion luminescence and temperature sensing properties of Ho3+/Gd3+ co-doped YbNbO4 phosphors

Abstract Ho3+/Gd3+ co-doped YbNbO4 phosphors were successfully synthesized by the high-temperature solid-state method. The crystal structure, morphology structure, element distribution, up-conversion luminescence and relative optical temperature sensing properties were investigated. X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM) analysis demonstrated that the doping of Ho3+/Gd3+ ions had no change in crystal structure and microstructure of YbNbO 4 phosphors. Under the excitation of 980 nm laser radiation, the green and red UC emissions were achieved by prepared phosphors, corresponding to the transitions of (5F4, 5S2)→5I8, 5F5→5I8 of Ho3+ ions. It is observed that the UC luminescence intensity was significantly enhanced for Ho3+/Gd3+ co-doped YbNbO4 samples compared to the mere Ho3+ doped YbNbO4 sample. Moreover, Ho3+/Gd3+ co-doped YbNbO4 samples' temperature sensitivity ranging from 303 to 663 K was calculated based on the fluorescence intensity ratio (FIR) method. The maximum sensitivity reached 0.0078 K−1 at 663 K. These results indicate that the YbNbO4:Ho3+/Gd3+ samples are a promising candidate for optical temperature sensing and up-conversion luminescence.