A Semi-Encapsulated Temperature Sensor Based on Er³⁺/Yb³⁺ Co-Doped Tellurite Fiber for Real-Time Low-Temperature Monitoring

In this study, a semi-encapsulated temperature sensor with simple structure based on Er<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>/Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> co-doped tellurite fiber was proposed for real-time low-temperature monitoring. The green and red up-conversion (UC) fluorescence peaks were observed at the center wavelengths of 532 nm, 545 nm, and 677 nm when pumped by a 980 nm semiconductor laser. The intensities of them showed a general decreasing trend with the temperature increasing from 253 K to 281 K. A high-precision nonlinear relationship between the values of 532 nm/545 nm and temperature was fitted using the fluorescence intensity ratio (FIR) technique, which has the excellent fitting result (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>=0.9934). Temperature sensing was further evaluated and its maximum absolute and relative sensitivities were calculated to be 0.00194 K<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 281 K and 0.01040 K<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 253 K, respectively. The fluctuations of FIR were 0.00255 and 0.00254 for long time operation at constant temperature of 266 K and 277 K, respectively. Finally, its response time was less than 2 s when the temperature jumped from 278.6 K to 273.8 K. The results showed that the fabricated temperature sensor has simple structure, high sensitivity, good stability and fast response time, which has great potential and promising application in the field of low-temperature monitoring.