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 YbNbO4 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.