Exploring new materials for optical thermometric sensing

The luminescence intensity ratio (LIR) of emission from two thermally coupled excited states is one of the most popular temperature sensing schemes, which has proven to be reliable due to its non-invasive nature, minimal dependence on the measurement conditions, and high temperature-spatial resolution. However, it requires a special design effort to obtain stable luminescence emission, which can be used for any practical application, for example, optical thermometric sensing. In this work, we present our results on the influence of excitation-emission processes on the dynamical behaviour of charges, and their temperature dependence in a wide temperature range (300-870 K), on a single crystal of EuPO4. The EuPO4 host which previously did not appear suitable for temperature sensing, was successfully converted to a highly sensitive optical temperature sensor, by following appropriate experimental strategy. The coupling of two excited states of Eu3+ showed a relative sensitivity of 2.00 %K-1, while, the coupling between two ground states of Eu3+ showed a relative sensitivity of 0.34 %K-1. The results suggest that by optimizing experimental parameters, highly sensitive optical thermometric sensors can be prepared, with ease.