Easily implementable time-resolved fluorescence intensity ratio approach for highly sensitive optical thermometry

Fluorescence intensity ratio (FIR)-based optical thermometry has attracted considerable attention owing to its self-calibrating ability and immunity to external interference during the measurement process. Herein, for further enhancing the relative sensitivity, a time-resolved FIR-based approach was proposed and successfully implemented employing a home-built time-resolved measurement system. By using the time-resolved FIR of Eu³⁺ to Mn⁴⁺ in BLN:1% Eu³⁺, 0.1% Mn⁴⁺ as the sensing parameter, drastic temperature dependence was obtained, and a maximum relative sensitivity of 7.8% K^-1 was achieved, which is remarkably superior to the FI- and lifetime-based methods with the identical sensing material. Excellent reversibility was also demonstrated by heating-cooling cycle tests. These findings indicate the great potential of the time-resolved FIR-based approach for high-performance optical thermometry.