Investigation of Thermal Sensing in Fluoroindate Yb³⁺/Er³⁺ Co-Doped Optical Fiber

An investigation of fluoroindate glass and fiber co-doped with Yb³⁺/Er³⁺ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs-²H_11/2 and ⁴S_3/2), non-thermally coupled levels (non-TCLs-⁴F_7/2 and ⁴F_9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K^-1-glass, 0.0019 K^-1-glass fiber ²H_11/2 → ⁴S_3/2 transition) and relative sensitivity (2.05% K^-1-glass, 1.64% K^-1-glass fiber ⁴F_7/2 → ⁴F_9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications.