Novel and High-Sensitive Primary and Self-Referencing Thermometers Based on the Excitation Spectra of Lanthanide Ions

Remote sensing through ratiometric luminescence thermometry based on trivalent lanthanide ions (Ln(III)) has lately become a promising technique due to its numerous applications. Most available Ln(III)-based luminescent thermometers require a calibration process with a reference thermal probe (secondary thermometers) and recurrent calibrations are mandatory, particularly when the thermometers are used in different media. This is sometimes impractical and a medium-independent calibration relation is postulated, which is potentially inaccurate. Thus, the determination of the temperature based on well-grounded physical principles by primary thermometers is the only way to overcome these challenges. Despite being considered one of the most important developments in luminescence thermometry, primary luminescent thermometers are scarce. Primary thermometers requiring calibration are proposed, implemented, and validated at one known temperature (primary-T), which are also self-referencing, employing ratiometric data from the excitation spectrum of Ln(III). By combining with the emission spectrum, thermometers not requiring calibration (primary-S) are devised. An Eu(III)-beta-diketonate complex is used as a proof-of-concept, but the approach is universal and other Ln(III)-based materials can be explored. Because many thermometric parameters are employed for temperature prediction an unprecedented very high accuracy of 0.2% in the physiological range is obtained.

Automated summary

Remote sensing through ratiometric luminescence thermometry based on trivalent lanthanide ions has become a promising technique with numerous applications. Most currently available luminescent thermometers require calibration with a reference thermal probe, but primary thermometers based on well-grounded physical principles are scarce. This study proposes and validates both calibrated primary thermometers and self-referencing thermometers using ratiometric data from the excitation spectrum of the lanthanide ions, achieving an unprecedented accuracy of 0.2% in the physiological range.