FLUORESCENCE CHARACTERISTICS OF CU-ZSM-5 ZEOLITES IN REACTIVE GAS-MIXTURES - MECHANISMS FOR A FIBER-OPTIC-BASED GAS SENSOR

In situ measurements of the fluorescence spectra, intensity, and respo nse time were made at elevated temperatures (similar to 500 degrees C) For samples of Cu-ZSM-5 exposed to dilute mixtures of O-2 in N-2 and to various O-2-reductant combinations in N-2. The results of these exp eriments are interpreted with a physical model of the oxidation/reduct ion kinetics of the copper ions. The fluorescence signal depends stron gly on the gas composition, providing a mechanism for a gas compositio n sensor. A prototype sensor configuration is described that uses a vi sible (488-nm) excitation source and la fiber-optic geometry to genera te and detect the fluorescence. The results indicate that for a weakly reducing gas the fluorescence signal correlates well with the oxygen concentration, whereas for strongly reducing gases the signal correlat es more closely with the reductant-to-oxidant ratio. (C) 1997 Optical Society of America.