An optical sensor for CO2 using thymol blue and europium(III) complex composite film

A new optical CO2 sensor based on the overlay of the CO2 induced absorbance change of pH indicator dye thymol blue with the luminescence of europium(III) complex, tris(thenoyltrifluoroacetonato) europium(III) dihydrate complex [(Eu(tta)3)] was developed. The observed luminescence intensity from [(Eu(tta)3)] at 613 nm increased with the increasing CO2 concentration. 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, respectively. The signal changes were fully reversible and hysterisis was not observed during the measurements.