During catalytic oxidation of the ethanol or acetone vapor adsorbed on the heated aluminium oxide (Al2O3) or barium sulfate activated by europium (BaSO42 : Eu) powder, a sustained emission of luminescence is observed. The profile of the band spectrum is dependent on the chemical species of the combustible vapor. This luminescence may be a kind of "adsorption luminescence" originating from the recombination of free carriers through the centers produced by the chemisorption of the gases. When the temperature of the specimen is kept over 380°C, the luminescence intensity is proportional to the combustible vapor concentration in air. The response is fast and reproducible for the change of sample gas. A gas sensor composed of Al2O3(or BaSO4: Eu) and an optical detector is applicable to the measurement of combustible gas mixtures.
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Nakagawa et al. (1990) studied this question.
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