Enhancement of oxygen/pressure sensing performance of Eu3+-doped YSZ phosphors via Bi3+ sensitization

The effects of the incorporation of a Bi³⁺ sensitizer on the phosphorescence properties and oxygen partial pressure sensitivity of the Eu³⁺ doped yttria stabilized zirconia (YSZ) phosphors were studied using a lifetime-based optical measurement system. Two series of YSZ: Eu phosphors were investigated in this work: Eu_0.01Bi_xY_0.07-xZr_0.92O_1.96 substitutional series and Eu_0.01Bi_xY_0.07Zr_0.92-xO_1.96-0.5x additive series. The phosphorescence intensity of the additive-series phosphors was enhanced by 47% excited at 405 nm with a Bi³⁺ concentration of 2 mol% due to the energy transfer between Bi³⁺ and Eu³⁺. In contrast, the phosphorescence intensity of the substitutional-series phosphors decreased as the Bi³⁺ concentration increased. The phosphorescence lifetimes for both series phosphors were highly sensitive to oxygen partial pressure at elevated temperatures. With increasing Bi³⁺ concentration, the oxygen sensitivities of both series were enhanced initially, which was related to the increment of concentration dependent non-radiative decay via cross-relaxation between Bi³⁺ and Eu³⁺. With 1 mol% Bi³⁺ doping, the oxygen sensitivity was enhanced by 28% and 12% for substitutional-series and additive-series phosphors, respectively. As the Bi³⁺ concentration further increased, the oxygen sensitivities of both series declined, which was attributed to the energy transfer between Bi³⁺, the formation of Bi³⁺ aggregates as well as the increase of the Eu³⁺ site symmetry. The results of this study not only provided valuable references for phosphor thermometry, but also offered new ideas for developing high-temperature non-contact pressure sensors.