Strong electron–phonon coupling of Cr3+ ion provides an opportunity for superior sensitivity cryogenic sensing

Nowadays, optical temperature measurement is becoming a reliable and advanced technology. Most of optical temperature sensing materials have been reported in the first biological temperature region or even higher. However, cryogenic optical sensing materials seem to be ignored. Here, Cr3+-doped SrGa12O19 is reported, exhibiting a obvious sharp peak at 696 nm (2E→4A2) and near-infrared emission at 750 nm (4T2→4A2) at 77 K. As the temperature increases, the transition of 2E→4A2 is suppressed and the emission of 4T2 is broadened due to the increasing electron–phonon coupling effect. This feature provides an opportunity to obtain the obvious discrepancy of fluorescence intensity, and further realize the superior cryogenic sensing performance based fluorescence intensity ratio (FIR) method with the maximum absolute sensitivity (Sa) of 0.0085 K−1 and relative sensitivity (Sr) of 2.62 %·K−1 at 77 K. The value of Sr is 138.6 % higher than that of CaHfO3:Cr3+ system and the temperature uncertainty (δT) is one order of magnitude lower than the most popular ruby Al2O3:Cr3+, showing superior cryogenic sensing ability. This work not only exhibits a novel cryogenic sensing material but also provides a train of thought for designing cryogenic thermometer.