A great variety of methods for oxygen sensing using luminescent sensors have been proposed in recent years based on intensity or in lifetime quenching. Like lifetime measurements, ratiometric techniques are insensitive to the variations of the excitation light, optical path and photo-bleaching. In this work we present a ratiometric method based on the phosphorescence-fluorescence spectral overlap emission of a phosphorescent chemical sensor. This dual emission makes ratiometric measurements possible without need of adding a reference luminophore. The ratio is calculated by measuring the phase shift between the excitation and the emission signal at two different frequencies. Theoretical aspects of the proposed methodology and the design and construction of a fiber-optical measuring system are discussed. Finally, the performance of the proposed measurement method has been assessed using the metal chelate Al-Ferron immobilized in an inorganic sol-gel support (an oxygen indicator which displays a strong fluorescence emission overlapping significantly with the measured phosphorescence emission).
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