Temperature-Driven Emission Redistribution of Yb²⁺ in SrB₄O₇ Enables Highly Sensitive Optical Thermometry Supported...

Optical thermometry is a modern, non-contact technique for temperature measurements, and its performance is fundamentally determined by the thermometric parameters employed. The use of unique luminescence from some divalent lanthanide ions may significantly boost the thermometric performance of optical sensors. Here, a first luminescent thermometer based on the rarely observed UV emission of Yb²⁺ is presented. The emitting lanthanide ions were successfully incorporated in the SrB₄O₇ host, whose thermal stability was confirmed in a broad T-range of ≈80-420 K. The material subjected to extreme temperature conditions manifests luminescence enhancement and spectral shifts toward both higher and lower energies, depending on the T-range studied. This is due to the thermalization processes within the excited electronic configuration 4f¹³5d¹ of Yb²⁺, leading to distinct temperature responses of different relaxation channels. The applied multiple linear regression (MLR) analysis allows the combination of different thermometric parameters and a multiple increase of the resulting temperature sensitivity. Importantly, the proposed lifetime-derived thermometric parameter, based on the decay-amplitudes ratio, results in the unprecedentedly high relative temperature sensitivity of 27.64 % K^-1. This approach provides a generalizable framework for extracting temperature information from luminescence dynamics in diverse phosphors, offering a new route for constructing high-performance optical thermometers.