An up-conversion Ba₃In(PO₄)₃:Er³⁺/Yb³⁺ phosphor that enables multi-mode temperature measurements and wide-gamut...

At present, most fluorescent materials that can be used for optical temperature measurement exhibit poor thermochromic performance, which limits their applications. In this study, the phosphor Ba₃In(PO₄)₃:Er/Yb was synthesized with a high doping concentration of Yb³⁺, and it emitted composition- and temperature-induced wide color gamut up-conversion luminescence from red to green. Four modes of fluorescence thermometry can be realized in the temperature range of 303-603 K, which is based on the ratio of fluorescence intensity between thermally coupled energy levels and non-thermally coupled energy levels, color coordinate shift, and fluorescence decay lifetime, respectively. The highest Sr value obtained was 0.977% K^-1. Taking advantage of the fact that temperature can significantly change the luminous color of the phosphor Ba₃In(PO₄)₃:0.02Er³⁺/0.05Yb³⁺, we demonstrated 'temperature mapping' on a smooth metal surface with multiple optical encryptions. These results indicate that the Ba₃In(PO₄)₃:Er/Yb phosphor is an excellent fluorescent material for thermal imaging and has great application potential in temperature visualization measurement and optical encryption.