Effect of Zn2+, S2−, Mo4+ and V5+ single doped BiTa7O19:Er3+/Yb3+ on upconversion luminescence intensity under 980 nm laser excitation

On the basis of BiTa7O19 (BTO):0.1Er3+/0.4Yb3+, Zn2+, S2−, Mo4+ and V5+ single doped upconversion phosphors (UCP) were successfully prepared by solid phase sintering. The lattice structure, particle size and diffuse reflectance spectra were measured by X-ray diffraction, scanning electron microscope and spectrophotometer. Upconversion luminescence (UCL) spectra of these UCP were investigated under 980 nm laser excitation with power density from 1.82 to 124.99 W/cm2. Zn2+ doped UCP can obtain the highest UCL intensity when excitation power density is less than 56.91 W/cm2, and Mo4+ doped UCP can obtain the highest UCL intensity when excitation power density is from 56.91 to 124.99 W/cm2. The UCL intensity of all samples increases first and then decreases with the increase of excitation power. By measuring UCL intensity changes with the excitation power of the UCP mixing with BN and UCP in vacuum and atmosphere, the experimental results show that the increase of temperature caused by laser excitation is the reason for the decrease of UCL intensity under high power excitation. Utilizing LIR technology, it is proven that at high power 90.95 W/cm2, Mo4+ and Zn2+ single doped can decrease and increase the UCP temperature under the same power density excitation compared with BTO:0.1Er3+/0.4Yb3+, respectively. The maximum relative temperature sensitivity of all UCP is calculated in the range of 0.00767–0.00854 K−1 at 303 K. All experiments show that Zn2+ and Mo4+ single-doped UCP are suitable for temperature sensing and luminescence imaging under low and high-power excitation, respectively.