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

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.