Energy Gap Linear Superposition of Thermally Coupled Levels toward Enhanced Relative Sensitivity of Ratiometric Thermometry.

Ratiometric luminescence thermometry (RLT) has attracted considerable attention for its non-invasive, fast response, and strong electromagnetic interference resistance; however, improving relative sensitivity ( S R ) is of great significance. Herein, we propose a design principle to promote S R by linearly superposing the energy gaps of thermally coupled levels (TCLs) subordinated to luminescence centers. A new fluorescence intensity ratio (FIR') is derived from multiplying the previous FIRs of multi-pair TCLs. Then, a new S R ' is significantly enhanced and proves to be the sum of the original S R values. The feasibility of this approach is proclaimed by applying to several materials [Na 0.5 La 0.5 TiO 3 :Yb/Nd, Y 2 O 3 :Yb/Er, and (LiMg) 2 Mo 3 O 12 :Yb/Er] with improved S R for RLT. Finally, a flexible film is fabricated for temperature measurement of actual scenes and manifests the superiority of the energy gap linear superposition method as ratiometric thermometry.