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

Abstract

ABSTRACT 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 LuVO 4 :25%Yb 3+ /Er 3+ ‐composite PICOF achieves record‐high accuracy (maximum absolute error δ max = 0.104°C), precision (standard deviation σ = 0.05°C), and temperature resolution ( T R = 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.