Detection of oxide-ion and oxygen vacancy swapping via upconversion luminescence in La2Mo2O9:Yb3+,Er3+

Abstract

It is requisite to detect thermally activated oxide-ion motion in oxide-ion conductors via an in situ non-contact method when applied in solid oxide fuel cells, oxygen sensors and oxygen separation. This research conceptually proposes an alternative approach by using the upconversion (UC) luminescence of Yb³⁺–Er³⁺ in La₂Mo₂O₉ oxide-ion conductors. According to the results, the temperature-dependent UC luminescence intensity ratio of ²H_11/2 → ⁴I_15/2 to ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ can reveal the activation process of oxide-ion and oxygen vacancy swapping at 150–200 °C in α-La₂Mo₂O₉, which has a break point in the plot. It is also evidenced and confirmed by the temperature-dependent UC decay curves, temperature-dependent alternating current (AC) impedance data, temperature-dependent internal friction data and temperature-dependent Raman data. The analysis according to Judd–Ofelt theory supports this point as well. This research may promote new applications of luminescence, and offer an alternative approach to design novel multifunctional materials.