Optical Temperature Sensor Based on Green Fluorescence of Er₂O₃ · 3Nb₂O₅ Phosphor

We report an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530- and 550-nm emissions of Er₂O₃ · 3Nb₂O₅ phosphor. The sensor consists of only a 980-nm LD, two narrow-band interference filters and two Si-photocells, while being without the use of optical lens to collect the fluorescence. Thermal effect on the photocell output was calibrated. The results show that the output has a linear relation to the temperature and the linearity is independent of input power. The performance characterization shows that the sensor exhibits a relative sensitivity (5-7) × 10^-3 K^-1 in the temperature range of 303-353 K. The setup is applicable to other Er³⁺-doped materials with a higher relative sensitivity.