A New Fluorescence Sensor for Quantification of Atmospheric Humidity

A new fiber-optic sensor (optrode) for humidity has been developed. The sensor utilizes a fluorescent dye entrapped within a perfluorinated ionomer matrix. The fluorescence intensity increases strongly and linearly with increasing water-vapor partial pressure even though the lifetime of fluorescence is simultaneously lowered. The response time of the optrode is approximately Is and the presence of CO₂ has no detectable effect on the determination of humidity. Apparently, the immobilized fluorescent dye, rhodamine 6G, associates with water to form a complex with a higher absorptivity. The dependence of fluorescence lifetime on emission wavelength revealed the coexistence of multiple excited states for the water-dye system.