Nowadays, by no means fortuitous, pollution-free and bio-regenerative solid oxide fuel cells (SOFCs) have arisen to be a competitive candidate as next generation renewable energy, which exhibiting high energy efficiency and flexible fuel choices. However, fast oxide-ion transportation of electrolyte could only be ensured in high working temperature by conventional views, which can decrease the voltage loss and further determine the electrical performance of SOFCs. Herein we report an in-situ and non-contact method to monitor the working condition of SOFCs and it is potential to become a promising optical temperature sensor to detect the working temperature of electrolyte materials. With the combinative protocol between density functional theory calculation and upconversion (UC) luminescence, the entanglement between thermal-driven formed O-ion Frenkel pair (native solubilizer) and Bi3+ dopant (competitive inhibitor) in La2Mo2O9 derivatives has been unraveled, especially at a lower temperature required by a future SOFCs device. It is a potential route for screening and characterizing the candidate electrolyte onsets in lower temperature without sacrificing electrical performance.