Synthesis of Barium Tungstate Up-Conversion Phosphor Applied in Temperature Sensing and Anti-Counterfeiting

Crystalline BaWO 4 was synthesized by preparing a precursor by co-precipitation followed by heat treatment at 800 °C. For use as up-conversion phosphor materials, rare earth ions Er 3+ and Yb 3+ were co-doped. In the synthesized BaWO 4 :[Er 3+ ]/[Yb 3+ ], a strong peak from the (112) phase, the main peak, could be observed in the XRD analysis and had a tetragonal structure. The lattice constant was changed by the rare earth doping, and when the sample was excited at 980 nm, green light emission was confirmed. The luminescence intensity changed according to the change in the amount of Er 3+ , a rare earth ion, and the luminescence intensity increased strongly as the laser power of the excitation wavelength increased. This is a phenomenon caused by the two-photon effect, and it was possible to confirm the characteristics of the up-conversion phosphor. To investigate the use of the synthesized phosphor for temperature sensors and anti-counterfeiting, a flexible composite and ink were made, respectively. As the temperature increased, the luminous intensity of the flexible composite was weakened, and the produced ink was difficult to observe with the naked eye when applied to banknotes, but when illuminated with a 980 nm laser, the green label could be seen.