AUTHOR=Martins Joana Costa , Skripka Artiom , Brites Carlos D. S. , Benayas Antonio , Ferreira Rute A. S. , Vetrone Fiorenzo , Carlos Luís D. 

TITLE=Upconverting nanoparticles as primary thermometers and power sensors

JOURNAL=Frontiers in Photonics

VOLUME=3

YEAR=2022

URL=https://www.frontiersin.org/journals/photonics/articles/10.3389/fphot.2022.1037473

DOI=10.3389/fphot.2022.1037473

ISSN=2673-6853

ABSTRACT=<p>Luminescence thermometry is a spectroscopic technique for remote temperature detection based on the thermal dependence of the luminescence of phosphors, presenting numerous applications ranging from biosciences to engineering. In this work, we use the Er<sup>3+</sup> emission of the NaGdF<sub>4</sub>/NaGdF<sub>4</sub>:Yb<sup>3+</sup>,Er<sup>3+</sup>/NaGdF<sub>4</sub> upconverting nanoparticles upon 980 nm laser excitation to determine simultaneously the absolute temperature and the excitation power density. The Er<sup>3+</sup><sup>2</sup>H<sub>11/2</sub>→<sup>4</sup>I<sub>15/2</sub> and <sup>4</sup>S<sub>3/2</sub>→<sup>4</sup>I<sub>15/2</sub> emission bands, which are commonly used for thermometric purposes, overlap with the <sup>2</sup>H<sub>9/2</sub> →<sup>4</sup>I<sub>13/2</sub> emission band, which can lead to erroneous temperature readout. Applying the concept of luminescent primary thermometry to resolve the overlapping Er<sup>3+</sup> transitions, a dual nanosensor synchronously measuring the temperature and the delivered laser pump power is successfully realized holding promising applications in laser-supported thermal therapies.</p>