High-sensitivity optical thermometry in Tb3+/Eu3+ co-doped Li2Y4(MoO4)7 phosphors synthesized via solid-state reaction

Abstract

Developing ratiometric optical thermometers with high sensitivity and signal stability remains a critical challenge in non-contact temperature sensing. Herein, a series of 5% Eu³⁺, 40% Tb³⁺ doped, and 40% Tb³⁺/5% Eu³⁺ co-doped Li₂Y₄(MoO₄)₇ (LiYMoO:Tb/Eu) phosphors were synthesized utilizing a conventional solid-state reaction route. Structural refinement and morphological inspections confirmed the phase purity and crystallinity of the resulting molybdate host. Under 325 nm ultraviolet excitation, the photoluminescence spectra revealed a multi-center emission profile, featuring characteristic transitions of Tb³⁺ (green) and Eu³⁺ (red) host framework, indicating an efficient energy transfer network among the dopants and the host. To evaluate the material's potential for thermometry, the fluorescence intensity ratio (FIR) technique was applied using the non-thermally coupled transitions of Tb³⁺ (⁵D₄ → ⁷F₅ at 542 nm) and Eu³⁺ (⁵D₀ → ⁷F₄ at 701 nm). The thermometric performance was investigated over the physiological and industrial temperature range of 300–403 K. Notably, the phosphor exhibited a superior maximum relative sensitivity (S_r) of 6.5% K⁻¹ at 300 K, significantly outperforming many existing molybdate-based sensors. These findings suggest that the 40% Tb³⁺/5% Eu³⁺ co-doped Li₂Y₄(MoO₄)₇ system is a promising candidate for precise optical temperature sensing applications.