Real-time monitoring of luminescent lifetime changes of PtOEP oxygen sensing film with LED/photodiode-based time-domain lifetime device

Abstract

A cost-effective LED/photodiode(PD)-based time-domain luminescent lifetime measuring device with rugged electronics and simplified algorithms was assembled and successfully used to characterize oxygen sensing films, by continuously monitoring phosphorescence lifetime changes of phosphorescent platinum octaethylporphyrin (PtOEP) in cardo poly(aryl ether ketone) polymer (IMPEK-C) vs. variation of the oxygen partial pressure in a gas mixture (O₂/N₂). The results determined by both phosphorescence lifetime and intensity monitoring were compared and the lifetime mode gave results which are in good agreement with the intensity mode. The lifetime-based linear Stern–Volmer plot indicates that the PtOEP molecules are nearly homogeneously distributed in the sensing film. The phosphorescent lifetime of the PtOEP film changes from 75 µs in neat N₂ to less than 2 µs in neat O₂. The sensing system (by combination of the PtOEP sensing film with the home-assembled lifetime device) gives a high lifetime-based O₂ sensing resolution, e.g. about 2 µs Torr⁻¹ for low O₂ concentration (below 3.5% O₂, V/V). This feasible lifetime device configuration is affordable to most sensor laboratories and the device may facilitate the study of O₂ sensing material with the continuous lifetime monitoring method.