Fiber optic fluorescence temperature sensors using up-conversion from rare-earth polymer composites

We demonstrate an optical fiber sensor based on the green up-conversion emission of rare-earth active ions hosted by a polymer matrix. The temperature sensitive composite material is fabricated by simple mixing of the rare-earth ions in powder form (NaY0.77Yb0.20Er0.03F4) with the polymer (polydimethylsiloxane). This fluorescent material is then incorporated on the tip of silica-glass optical fibers to obtain a point temperature sensor probe. Temperature measurements are obtained through the fluorescent intensity ratio technique, yielding a linear response and minimizing spurious effects on the up-conversion fluorescence signal. The fiber sensors fabricated with this material provide good performance within a temperature range of 20–100°C, excellent linearity (r2=0.999), and good thermal and fluorescent stability.