Influence of dysprosium concentration on sensitivity of luminescent thermometers of phosphors Ca_9Tb(PO_4)_5(SiO_4)F_2

Tb³⁺,Dy³⁺-co-doped Ca₉Tb_xDy_1–x(PO₄)₅(SiO₄)F₂ phosphors were prepared via high-temperature solid-phase reaction method and the potential application in optical temperature measurements due to their color-tunable property was investigated in detail. The photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra results show that the as-prepared phosphors exhibit both Tb³⁺ and Dy³⁺ emissions at 546 nm (⁵D₄–⁷F₅ transition of Tb³⁺) and 587 nm (⁴F_9/2–⁶H_13/2 transition of Dy³⁺) upon 376 nm excitation, respectively. In addition, the fluorescence decay analysis shows that the lifetime of the Tb³⁺ emission rapidly decreases, which confirms the energy transfer existence between Dy³⁺ and Tb³⁺. Under 376 nm excitation, the temperature dependence of the fluorescence intensity ratios for the dual-mission bands peaked at 546 and 587 nm was studied in the temperature range from 303 to 573 K. The results show that with the increase of Dy³⁺ concentration, the relative sensitivity first increases and then decreases, what's more, the maximum relative sensitivity is 3.142 × 10^?3%/K for Ca₉Tb_xDy_1–x(PO₄)₅(SiO₄)-F₂ (x = 0.4). As a consequence, this preliminary study provides a novel method for exploring the novel thermometers.