Development of a fluorescence lifetime-based sol–gel humidity sensor

A sol–gel-based optical sensor for the measurement of relative humidity has been developed. It is based on the changes in fluorescence intensity and/or lifetime of the ruthenium complex, ruthenium(II)diphenylphenanthroline-dipyridophenazinehexafluorophosphate. Sensitivity to relative humidity has been demonstrated over the range 0–100% relative humidity. This sensor has been developed for application in the field of indoor air-quality monitoring and displays a limit of detection of 0.35% relative humidity and a resolution of 1.13% over the concentration range of interest (0–50% relative humidity). The effects of varying process parameters on the sensor performance were studied along with the effects of cross-sensitivity to molecular oxygen.