Three-energy-level-cascaded strategy for a more sensitive luminescence ratiometric thermometry

Abstract Luminescence ratiometric thermometry has gained increasing attention in recent years because of its several merits, such as non-invasive operating mode, fast response time, excellent spatial resolution, and so forth. It can be realized by using the thermally coupled energy levels (TCELs) of rare earth ions. The maximum thermal sensitivity for the TCELs-based luminescence ratiometric thermometry has been found to be ∼2000/kT2. Here we show that using a three-energy-level-cascaded strategy can surpass this maximum value. In scheelite host material, the 4G11/2-6H15/2 transition of Dy3+ ion was observed successfully upon UV excitation. Moreover, the Dy3+ ion’s 4G11/2/4I15/2/4F9/2 excited states were confirmed to be thermally linked with each other by studying on the photoluminescence of the as-prepared Dy3+-embedded phosphors at different temperatures. By utilizing the 4G11/2/4F9/2 states, rather than the commonly investigated 4I15/2/4F9/2 ones in the previous literatures, the relative sensitivity was found to as high as 2414/kT2 over the experimental temperature range. It surpasses the theoretical maximum value 2000/kT2. In the end, we study the relationship between the relative sensitivity and temperature resolution, and find that a higher relative sensitivity cannot always ensure a better temperature resolution. In order to achieve a better temperature resolution in practice, both the relative sensitivity and the relative uncertainty of the luminescence intensity ratio that is used for indicating temperature should be considered simultaneously.