High-sensitive temperature sensing use NIR upconversion luminescence of Er³⁺-core@Tm³⁺-shell with good robustness

In recent years, lanthanide doped materials have been extensively studied in the field of fluorescence temper-ature sensing due to their abundant emission levels and sensitive thermal response. Temperature sensing based on fluorescence intensity ratio (FIR) of upconversion nanoparticles has the advantages of fast temperature response, non-aggressiveness, and high spatial resolution. However, the most reported FIR sensing has limited sensitivity, probably due to the use of thermal coupling levels. Herein, we report a novel FIR temperature measurement based on non-thermal coupling levels of NaGdF4:Yb3+/Er3+@NaGdF4@NaGdF4:Yb3+/Tm3+ core-shell-shell nanostructure, which has high sensitivity and robustness simultaneously. The relative sensitivity based on I801/I654 and I801/I841 of Tm3+ to Er3+ can reach up to 4.56 (303 K) and 3.82% K-1 (313 K), respectively. Between them, FIR of I801/I841 is independent of excitation power and time. These results show the great po-tential of FIR based on non-thermal coupling levels in high-sensitive and robust temperature sensors.