Optical temperature sensing by tuning photoluminescence in a wide (visible to near infrared) wavelength range in a Eu-doped Bi-based relaxor ferroelectric.

The prevalent material design principles for optical thermometry primarily rely on thermally driven changes in the relative intensities of the thermally coupled levels (TCLs) of rare-earth-doped phosphor materials, where the maximum achievable sensitivity is limited by the energy gap between the TCLs. In this work, a new, to the best of our knowledge, approach to thermometric material design is proposed, which is based on temperature tuning of PL emission from the visible to the NIR region. We demonstrate a model ferroelectric phosphor, Eu-doped 0.94(NaBiTiO)-0.06(BaTiO) (NBT-6BT), which, by virtue of the contrasting effects of temperature on PL signals from the host and Eu intraband transitions, can achieve a relative thermal sensitivity as high as 3.05% K. This model system provides a promising alternative route for developing self-referencing optical thermometers with high thermal sensitivity and good signal discriminability.