Facile preparation of upconversion microfibers for efficient luminescence and distributed temperature measurement

Abstract

Accurate temperature measurements with high spatial resolution are required in many fields to monitor integrated circuits and study biological cells. However, it is challenging to measure distributed temperature with high spatial resolution. In this study, microfibers comprising upconversion nanoparticles (UCNPs) and polymethyl methacrylate (PMMA) were fabricated by a facile solution drawing method. The presented microfibers range in diameter from 2.5 to 15 μm and have a uniform length of hundreds of microns. We measured the transmission loss and evanescent coupling levels to demonstrate that these microfibers (UCNP/PMMA) have optical waveguide properties and coupling characteristics under laser excitation at 980 nm. Using fluorescence intensity ratio (FIR) technology, we investigated the photothermal properties of these microfibers (UCNP/PMMA) for temperature sensing, and experimentally and theoretically derived the temperature at different locations of the microfiber from a single heat source, thus realizing distributed temperature measurement with a high spatial resolution of 10 μm. The maximum sensitivity was measured as 0.00935 K⁻¹ at 299 K, and the error range of the distributed temperature was less than 2 K. The results indicate that the presented microfibers are a promising candidate for use in an optically distributed temperature sensor with high spatial resolution.