Fluorescent Optical Fiber Intensity Ratio Temperature Sensor Based on Polymer Matrix Using Down-Conversion From ZnS:Cu

Aiming at the problem of long-term dependence on rare-earth (RE) ions and insufficient stability of a fluorescent optical fiber temperature sensor, a fluorescence intensity ratio (FIR) temperature sensor based on ZnS:Cu was proposed. ZnS:Cu powder is adhered to the end face of multimode quartz fiber by blending into polydimethylsiloxane (PDMS). PDMS improves the coupling efficiency between fluorescence and quartz fiber and provides sufficient adhesion for the powder. Benefiting from the temperature dependence of ZnS:Cu, the intensity ratio of the two down-conversion (DC) luminescence bands excited by ultraviolet (UV) varies with temperature. The results of experimental verification confirm that the sensor has excellent linear response ( $R^{2} =0.991$ ), stability, and repeatability in the temperature range of 20.1 °C–101 °C, with an average temperature sensitivity of −0.00515 °C ⁻¹ . These characteristics show that the designed sensor has great potential in temperature sensing applications, and the proposed ZnS:Cu, which can replace RE ions, is an excellent candidate for the fluorescent optical fiber temperature sensor.