Cr3+‐Facilitated Ultra‐Sensitive Luminescence Ratiometric Thermometry at Cryogenic Temperature

Abstract Non‐contact ratiometric luminescence thermometry continues to gain popularity over decades due to its fascinating features of high accuracy, fast response, and simplicity. In this regard, rational design of optical thermometers with ultrahigh relative sensitivity and low temperature resolution has become a cutting‐edge topic. Herein, a luminescence intensity ratio thermometric method depending on the emission line at 698 nm (peak 1) and the emission bands at 713 and 721 nm (peaks 2 and 3) of Li 1.97 Zn 1.0292 Ge 3 O 8 :0.08%Cr 3+ is proposed. As temperature elevates from 50 to 300 K, the 698 nm emission line undergoes an 84‐fold increase while the 713 and 721 nm emission bands show the opposite decline trend. This fascinating feature enables high relative sensitivity of 13.09% K −1 and low temperature resolution of 0.032 K, which are superior to most of the reported optical thermometers. This work is expected to provide more insights for designing excellent and reliable optical thermometers by employing Cr 3+ activated luminescent materials.