Fig. 2. Normalized absorption and emission spectra of the secondary emitter Ir(CS)2(acac) (gray solid). Normalized absorption spectra of crystal violet (black dashed) and the basic and acidic form of m-cresol purple (black solid) employed in the carbon dioxide sensor. Crystal violet (used for distance-dependent measurements) and basic m-cresol purple (Ind–) show good spectral overlap with the emission of the secondary emitter dye resulting in strong absorption of the guided light. On exposure of the sensor to carbon dioxide the basic band disappears, while the acidic band appears and leads to decreased absorption of the guided light.
