Oxygen sensitivity of ruthenium-doped sol-gel derived silica films

The feasibility of an oxygen sensor based on the quenching of fluorescence of ruthenium complexes in the presence of oxygen was investigated. Porous sol-gel derived silica thin films deposited on a glass substrate by a dip-coating technique were impregnated with the fluorescent complexes Ruthenium(2,2-bipyridene)3++ and Ruthenium (4,7- diphenylphenanthroline) 3++. Sol-gel film thickness, chemical composition and concentration of the fluorescent species within the film were optimised. The samples were excited by a CW Argon ion laser (Aex = 488nm) for fluorescent intensity measurements, and by a pulsed Nd- Yag laser (kex = 532nm) for lifetime measurements. For each complex, both the fluorescent intensity and lifetime were quenched by oxygen. The optical decay times were analysed using two methods: (a) Numerical Integration, and (b) Line stripping. Method (b) was favoured, and involved analysis in terms of one quenched and one unquenched fluorophore component, the latter arising from the fraction of ruthenium complex molecules which were inaccessible to oxygen. By taking intensity and lifetime measurements for known oxygen concentrations from 0 to 10 0 %, intensity and decay time Stem-Volmer plots were produced for both complexes. The performance of both ruthenium complexes was compared and contrasted, and their suitability for use in optical oxygen sensors based on sol-gel entrapped fluorescent molecules was discussed