Bandwidth-based flexible optical fiber thermometry based on sharp line emission regulation of Cr3+ ions

We designed and fabricated a flexible optical fiber based on LiGa4(MgGe)0.5O8:Cr phosphors with temperature-dependent fluorescence characteristics. Specifically, the full width at half maximum (FWHM) of the emission band broadens with elevated temperature due to the increased electron–phonon interactions in the matrix. Moreover, the FWHM values subtly increase with the increase in the concentration of the [Mg2+–Ge4+] unit in LiGa4(MgGe)0.5O8:Cr, along with the increase in the external quantum efficiency from 24.8% to 50.0%. Furthermore, these phosphors exhibit excellent luminescence thermal resistance, with an outstanding absolute sensitivity of 7.51 cm−1 K−1 at 443 K and a good relative sensitivity of 0.64% K−1 at 303 K. Finally, a flexible all-fiber system is employed to monitor the real-time temperature of objects with excellent repeatability, precision, and stability. This work not only explores the promising application of Cr3+-doped luminescent materials with sharp emissions but also enriches the new routes of optical temperature measurement owing to the bandwidth characteristics.