Optical CO2 Sensor with the Combination of Colorimetric Change of pH Indicator and Internal Reference Luminescent Dye

A new optical CO2 sensor based on luminescence intensity changes of europium(III) complex, tris(thenoyltrifluoroacetonato)europium(III) dihydrate complex ([Eu (tta)3]) due to the absorption change of pH-indicator dye (thymol blue) with CO2 was developed and its CO2 sensing properties were investigated. The observed luminescence intensity (I) from [Eu(tta)3] at 613 nm increased with increasing the CO2 concentration. The ratio I0/I100, where I0 and I100 represent the detected luminescence intensities from a layer exposed to 100% nitrogen and 100% CO2, respectively, that we takes the sensitivity of the sensor is estimated to be 16.0. The response times of the sensing film were 4.0 s for switching from nitrogen to CO2, and 36 s for switching from CO2 to nitrogen. The signal changes were fully reversible and no hysterisis was observed during the measurements.