Lanthanide doped BaTiO₃−SrTiO₃ solid-solution phosphors: Structure, optical spectroscopy and upconverted temperature sensing behavior

Lanthanide doped Ba_1-xSr_xTiO₃ (x = 0–1) solid-solution phosphors were successfully prepared by a conventional solid-state reaction. Using Eu³⁺ dopants as the structural probe, the variation of ⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁ emission intensity ratio with increase of Eu³⁺ content and the excitation-wavelength-dependent luminescence in the Ba_1-xSr_xTiO₃ sample were demonstrated to be originated from the different emission behaviors of Eu³⁺ in Ba²⁺/Sr²⁺ site and Ti⁴⁺ site. Furthermore, upconversion luminescence for the Yb³⁺/Er³⁺ co-doped Ba_1-xSr_xTiO₃ samples were investigated, and it was found that the emission intensity of Yb³⁺/Er³⁺: Ba_0.5Sr_0.5TiO₃ phosphor was about 5 and 2 times as high as those of Yb³⁺/Er³⁺: BaTiO₃ and Yb³⁺/Er³⁺: SrTiO₃ ones. Using the investigated Yb³⁺/Er³⁺: Ba_0.5Sr_0.5TiO₃ solid-solution as the optical thermometric medium, the temperature sensitivity was determined to be 0.76% K⁻¹ at the temperature of 610 K based on the temperature-dependent fluorescence intensity ratio of the thermally coupled ²H_11/2 and ⁴S_3/2 emitting-states of Er³⁺. - Highlights: • Lanthanide doped Ba_1-xSr_xTiO₃ (x = 0–1) solid-solutions were fabricated. • Excitation-wavelength-dependent Eu³⁺ emissions were recorded. • Enhanced Er³⁺ luminescence was realized by partial substitution of Ba²⁺ by Sr²⁺. • T-sensitive emissions of two Er³⁺ thermally coupled states were observed. • The upconversion phosphor exhibited a high sensitivity of 0.76% K⁻¹.