Suppressing Photothermal Artifacts in Flexible Fluorescent Fiber-Optic Sensors for Accurate and Precise In Situ Temperature Monitoring.

Ratiometric flexible fluorescent fiber-optic sensors, featuring self-calibration and precise spatial localization, are emerging as a robust platform for in situ thermal monitoring, advancing applications such as battery safety management and biomedical diagnostics. However, measurement artifacts induced by the inherent photothermal effect remain largely overlooked, posing a challenge to high-accuracy temperature sensing. Here, we propose a partial-inner-cladding optical fiber (PICOF) to suppress photothermal artifacts by isolating the sensing layer from the coupling interface and the fiber core, where self-heating predominantly occurs. Compared with conventional fiber structures, the PICOF extends the allowable excitation power from ≤ 15 to 61 mW and improves the luminescence signal-to-noise ratio from 36.6 to 42 dB, enabling high-fidelity readout with a relative standard deviation below 0.09% even under power fluctuations and deformation disturbances. Consequently, the LuVO4:25%Yb3+/Er3+-composite PICOF achieves record-high accuracy (maximum absolute error δmax = 0.104°C), precision (standard deviation σ = 0.05°C), and temperature resolution (TR = 0.2°C) among reported fluorescent fiber-optic sensors. Furthermore, practical demonstrations underscore its utility for early warning of thermal hazards and incipient failure in sodium-ion batteries, and as an in situ diagnostic reference for the Bárány caloric test. This work provides an effective and generalizable strategy for the advancement of high-accuracy fluorescent thermometry.