Unconventional use of mixed-phase TiO2 as optical gauge of molecular oxygen with ratiometric-enhanced responsivity

We show that mixed-phase (MP) titanium dioxide (TiO2) can be effectively employed as an unconventional, inorganic, dual-emitting and ratiometric optical sensor of O2. Thanks to the peculiar "anti-correlated" photoluminescence of the two TiO2 crystal phases, MP-TiO2 exhibits an unusual ratiometric-enhanced responsivity. Simultaneous availability of rutile and anatase TiO2 PL allows using their ratio as measurement parameter associated to O2 concentration, leading to larger experimental responsivity compared to the one obtainable for single-phase PL detection. A proof of this concept is given, showing a two-fold enhancement of the optical responsivity. Additional characteristics of mixed phase TiO2 can be envisaged as favorable for O2 optical probing, namely: (a) low production costs, (b) absence of heterogeneous components, (c) self-supporting properties. These characteristics promote testing mixed phase TiO2 use for applications requiring high indicator quantities at competitive price, possibly also tackling the need to develop supporting matrixes that carry the luminescent probes and avoiding issues related to the use of different components for ratiometric sensing.