Highly sensitive dual-mode thermometry over a wide temperature range based on bandgap engineering in LiNb_1-xTa_xO₃:Tb³⁺

Having proved that highly sensitive dual-mode optical thermometry could be implemented based on fluorescence intensity ratio (FIR) of the same green emission driven by varying excitations and fluorescence lifetime (FL) of Tb3+, the feasibility to manage thermometric performance over a wide temperature range via bandgap engineering is validated in LiNb(1-x)TaxO(3):Tb3+. The vital thermally activated relaxation processes via an intervalence charge transfer state are altered by formulating crystal structure via partial replacement of Nb5+ with Ta5+, allowing adjustment of the sensitive temperature range which can be measured with the highest accuracy. Specifically, maximum relative sensitivities SR up to 1.43 and 2.36 %K-1 are respectively attained in FIR and FL modes of LiNb1.0Ta0.0O3:Tb3+. The upper limit of the sensitive temperature range is proved to be greatly extended from 260 to 440 K for LiNb0.2Ta0.8O3:Tb3+. This work may provide a perspective approach to design self-calibrated thermometers targeted at different temperature ranges for varying applications.