Up-conversion luminescence properties and temperature sensing characteristics of Tm3+, Yb3+ co-doped SrBi4Ti4O15 phosphors with high thermometric sensitivity

In this work, Tm³⁺- and Yb³⁺-doped SrBi₄Ti₄O₁₅ phosphor was successfully synthesized through the high-temperature solid-state reaction. The phosphor composition was characterized by X‑ray diffraction, revealing a reduction in the lattice parameters and volume due to a successful substitution of Sr³⁺ by Tm³⁺ and Yb³⁺. Under the excitation of a 980 nm diode laser, weak green emission centered at 476 nm and strong red emission centered at 696 and 801 nm were observed, which originated from Tm^{3+ 1}G₄→³H₆, ¹G₄→³F₄, ³F_2,3→³H₅ and ³H₄→³H₆ transitions. The best doping concentration for Tm³⁺ and Yb³⁺ was 1 and 20 mol%, respectively. Extensive studies were conducted on the Tm³⁺/Yb³⁺ co-doping effect on the pump power. The absolute sensitivity of non-thermal coupling levels for doped Tm³⁺/Yb³⁺ calculated at different wavelengths, was 0.4504 and 0.0359 K⁻¹, respectively. These results indicated that SrBi₄Ti₄O₁₅:Tm³⁺/Yb³⁺ is an effective candidate for red up-conversion luminescent materials and can be used as a high-efficiency temperature sensing material.