Extremely intense pure green upconversion luminescence in Ho³⁺/Yb³⁺ co-doped BiTa₇O₁₉ phosphors under 980 nm laser excitation

A series of BiTa₇O₁₉(BTO):Ho³⁺/Yb³⁺ phosphors were prepared by high-temperature solid state sintering, which exhibited outstanding pure green upconversion luminescence (UCL) under 980 nm laser excitation. When Ho³⁺ doping 10 mol%, Yb³⁺ has almost no concentration quenching point. By optimizing the preparation process, the phase purity of the sample can be improved. Under 980 nm laser excitation power density of 124.99 W/cm², the UCL intensity of the optimized sample is 1.79 times that of the non-optimized sample. The maximum relative temperature sensitivity S_R of 0.384% K⁻¹ at 557 K and 0.40% K⁻¹ at 723 K can be obtained by using luminescence intensity ratio (LIR) technique. All experiments show that BTO is an excellent UCL host, and BTO:Ho³⁺/Yb³⁺ can be used in UCL display and temperature sensing.