Photoluminescence-based gas sensing with rare-earth doped titania

During the last decade, some metal oxide nanomaterials have been found to possess a gas sensitive photoluminescence (PL). The presentation focuses on Sm- and Nd-doped TiO2 nanopowders and thin films, which PL can be effectively excited via band-to-band transition. The gas sensitivity of PL was systematically studied in a wide range of oxygen concentrations in air, ranging from 50 ppm to 100%, and at ppm-levels with other gases (NH3, NO2). An original physical model was developed for sensing mechanism, which involves three “players”: rare-earth ion, internal defect, and adsorbed gas molecule; and two processes: the resonant energy transfer between the rare-earth ion and the internal defect, and the electron transfer between the internal defect and the gas molecule. We also showed that significantly higher measurement accuracy and reduced long-term drift can be achieved by combining different simultaneously recorded sensor signals - rare-earth PL, intrinsic PL, and electrical conductance. Such an integration of optical and electrical readouts may be a promising development leading to novel sensor platforms.