Eriochrome cyanine doped sol–gel coatings. Optical behavior against pH

Sol-gel silica coatings doped with eriochrome cyanine (EC) have been prepared upon soda lime glass substrates by dip-coating. Sols were obtained starting from a silicon alkoxide hydrolysed in acid medium. EC was added to the silica sol dissolved in water and methyl alcohol to reach 1% of the total weight. Dried coatings showed pH-sensitivity (change of optical absorption and luminescence) when dipped into liquids as well as when exposed to aqueous gases at different pH. On this basis, EC doped coatings could be used as optical sensors, for instance, in analytical probes. Coatings have been demonstrated to be stable enough to UV radiation, at least at handling temperature to be used for optical sensors in common analytical instrumentation. Additional tests pointed out the behaviour of coatings to different chemical media at temperatures below 100°C. Adherence of coatings was evaluated by scratching and peeling, as well as dipping the samples into a cleaner solution submitted to ultrasounds.