Effect of Li+/K+/Zn2+ doping on the optical and temperature sensing properties of Tm3+ and Yb3+ doped YVO4 phosphor

Abstract

The Pechini sol-gel reaction technique has been used to produce Tm3+, Yb3+ co-doped YVO4 and Li+/K+/Zn2+ codoped YVO4: Tm3+,Yb3+ phosphors. Post-heat treatment (at 800 °C) was given to all the samples to strengthen the material's structural and optical characteristics. Prepared phosphors exhibit blue and near-infrared (NIR) light. The crystalline structure and morphology of the prepared phosphors were studied by using powder X-ray diffraction (PXRD), Fourier transform Infrared spectroscopy (FTIR) and scanning electron microscope (SEM). All prepared phosphors crystallise in the tetragonal crystal structure having space group I41/amd. Prepared phosphors, when pumped with the laser at 980 nm, give strong upconversion emission in blue and NIR regions that correspond to Tm3+ transitions 1G4→3H6 and 3H4→3H6, respectively. Li+/K+/Zn2+ co-doping enhances the luminescence intensity significantly. Among Li+/K+/Zn2+ ions, Zn2+ co-doping increases the upconversion emission intensity mostly compared to others, the blue emission intensity get increased by ∼7 times and the NIR by ∼6 times. The main cause of enhancement in the emission intensity may be primarily due to the charge imbalance and asymmetry in the crystal field.Further, optical temperature sensing was also investigated by using the fluorescence intensity ratio (FIR) of the transitions (3F2,3→3H6) and (3H4→3H6). Co-doping of Li+/K+/Zn2+ ions also affects the temperature sensitivity. The relative sensitivity and absolute sensitivity of the samples were also calculated. This study indicates that this phosphor is a suitable candidate as a blue phosphor for display devices, WLEDs and optical temperature-sensing probes.