Dual-functional application of Ca₂Ta₂O₇:Bi³⁺/Eu³⁺ phosphors in multicolor tunable optical thermometry and WLED

A series of Bi³⁺/Eu³⁺ co-doped Ca₂Ta₂O₇ (CTO:Bi³⁺/Eu³⁺) phosphors were prepared by high-temperature solid-state method for dual-emission center optical thermometers and white light-emitting diode (WLED) device. By modulating the doping ratio of Bi³⁺/Eu³⁺ and utilizing the energy transfer from Bi³⁺ to Eu³⁺, the tunable color emission ranging from green to reddish-orange was realized. The designed CTO:0.04Bi³⁺/Eu³⁺ optical thermometers exhibit significant thermochromism, superior stability, and repeatability, with maximum sensitivities of S_a = 0.055 K^-1 (at 510 K) and S_r = 1.298% K^-1 (at 480 K) within the temperature range of 300-510 K, owing to the different thermal quenching behaviors between Bi³⁺ and Eu³⁺ ions. These features indicate the potential application prospects of the prepared samples in visualized thermometer or high-temperature safety marking. Furthermore, leveraging the excellent zero-thermal-quenching performance, outstanding acid/alkali resistance, and color stability of CTO:0.04Bi³⁺/0.16Eu³⁺ phosphor, a WLED device with a high R_a value of 95.3 has been realized through its combination with commercially available blue and green phosphors, thereby demonstrating the potential application of CTO:0.04Bi³⁺/0.16Eu³⁺ in near-UV pumped WLED devices.