Abstract

Fluorescence-based and luminescence-based humidity sensors, discussed in the present chapter, are the third main type of optical humidity sensors. These sensors were derived from the phenomenon that water molecules are able to influence the fluorescence or luminescence emission of certain compounds. With the increasing relative humidity, either an enhancement or a quenching of the fluorescence intensity of a humidity-indicator dye was observed. This chapter gives a detailed description of both the principles of the operation of such sensors, and fluorescence dyes, which can be used in these devices. Perylene dyes, Rhodamine 6G, Fluorescein dye, Pd– and Pt–porphyrin dyes, and many other ones are acceptable for design of fluorescence-based humidity sensors. Advantages and disadvantages of fluorescence- and luminescence-based humidity sensors are also discussed in the present chapter. One should note that the configuration of fluorescence-based humidity sensors generally produces a rapid response because it requires only a very thin reagent coating (about a few ?m thick) and promotes an efficient mass transfer during the interaction with the analyte.