“Oxygen quenching” in Eu-based thermographic phosphors: Mechanism and potential application in oxygen/pressure sensing

The effect of ambient oxygen concentration on thermographic phosphor thermometry was investigated to uncover the “oxygen quenching” mechanism of Eu-based phosphors using a lifetime-based measurement system. The phosphors being studied were the Eu doped yttria stabilized zirconias (YSZs) with Y3+ concentrations of 0, 8, 12 and 57 mol%, having monoclinic, tetragonal, cubic and δ crystalline lattice, respectively. To vary the ambient oxygen concentration, three different gas phases (air, oxygen and nitrogen with methane) were used. It was found that the phosphorescent lifetimes and intensities of all four phosphors were sensitive to the ambient oxygen concentration, while the reference phosphor, Y2SiO5:Eu, was not influenced. The “oxygen quenching” phenomenon observed in Eu-doped YSZs was attributed to the oxygen vacancies in the phosphors. In addition, the four YSZ:Eu phosphors exhibited different sensitivity to ambient oxygen concentration. The oxygen sensitivity was found to be closely related to the site symmetry of Eu3+, which was previously determined by the phosphorescent spectra. The site symmetry of Eu3+ strongly affected the charge-transfer states and therefore determined the non-radiative decay rate. The current findings provided guidance for the phosphor selection and sensor design for oxygen/pressure sensing in high-temperature environment.