Dual‐Mode Optical Temperature Sensing of Mg 0.75 Al 2.16 O 4 : Cr 3 Bowen Chen, Min Ni, Chunbo Dai, Hao Wang, Bingtian Tu, Weimin Wang, Zhengyi Fu
ABSTRACT
Designing the energy transfer process between activator ions is an effective strategy for achieving multimodal, high‐sensitivity fluorescent temperature sensing. Herein, a dual‐mode fluorescent temperature sensor was developed based on the Mg 0.75 Al 2.16 O 4 : 0.1at%Cr 3+ /0.03at%Er 3+ transparent ceramic. Spatial separation of Cr 3+ /Er 3+ ions was achieved by utilizing both the lattice and grain boundary environments within the transparent ceramic. Within this unique structure, efficient energy transfer from Er 3+ to Cr 3+ was established. As a result, Cr 3+ emitted near‐infrared upconversion fluorescence peaking at 797 nm ( 4 T 2 level) under 980 nm laser excitation. The downconversion fluorescence lifetime of Cr 3+ and the upconversion fluorescence intensity ratio of Cr 3+ /Er 3+ can serve as temperature sensing signals. Within the range of 300–573 K, the maximum relative sensitivity reached 4.2% K −1 . This work demonstrates the potential for designing functional ionic spatial structures within transparent ceramics.