Up‐Conversion Luminescence and Optical Temperature Sensing Properties of Er,Yb Co‐Doped Al ₂ O ₃ ‐YAG Ceramics

A novel series of Er 3+ ,Yb 3+ co‐doped Al 2 O 3 ‐YAG composite ceramics was synthesized via high‐temperature solid‐state reaction for optical thermometry applications. The ceramics exhibit stable up‐conversion luminescence under 980 nm excitation, with green emissions originating from the thermally coupled levels ( 2 H 11/2 and 4 S 3/2 ) of Er 3+ . The fluorescence intensity ratio (FIR) of these transitions follows Boltzmann distribution, enabling temperature sensing from 293 to 493 K. Maximum relative and absolute sensitivities reached 0.9% K −1 at 293 K and 0.2% K −1 at 493 K, respectively. The results demonstrate that Er 3+ ,Yb 3+ :Al 2 O 3 ‐YAG ceramics are promising candidates for high‐temperature optical thermometry due to their stability, sensitivity, and robust physicochemical properties.