NIR‐to‐NIR Lifetime Based Thermometry with the Thermally Elongated Luminescence Kinetics Driven by Structural Phase Transition in LiYO2:Yb3+

Abstract Among the various techniques used in luminescence thermometry, luminescence kinetics is considered the least sensitive to perturbations related to the optical properties of the medium containing the phosphor. For this reason, temperature sensing and imaging using lifetime‐based luminescence thermometers are of high interest for a wide range of specific applications. However, for most such thermometers, an increase in temperature leads to a shortening in lifetime, which can hinder the specificity and accuracy of the readout. In this work, an approach is presented that utilizes a thermally induced increase in the symmetry of the host material associated with a structural phase transition in LiYO 2 :Yb 3+ . Consequently, the lifetime of the excited level 2 F 5/2 of the Yb 3+ ion is thermally prolonged, achieving a relative sensitivity of 0.5%/K. The phase transition temperature can be controlled by adjusting the dopant concentration. Additionally, thermal changes in the emission spectrum enable the use of LiYO 2 :Yb 3+ for ratiometric temperature readout with a relative sensitivity of 5.3%/K at 280K for LiYO 2 :5%Yb 3+ .