Abstracts
Luminescent materials for imaging, sensors and theranostics
Beyond the single parametric thermal sensing: Unifying thermometric parameters to improve the performance of EuIII-based luminescent thermometersLeonardo F. Saraiva1, Airton G. B. Jr.2, Fernando A. Sigoli2, S. A. M. Lima3, Ana M. Pires3
1São Paulo State University (UNESP), Department of Chemistry and Biochemistry, Brazil., 2Institute of Chemistry, Campinas University, 3São Paulo State University (UNESP)
E-mail: leonardo.f.saraiva@unesp.br
The physical quantity that measures the thermal energy of a body is one of the definitions of temperature, which is the most fundamental thermodynamic state variable. Its fluctuations are central to myriad natural and man-made operations, such as life-sustaining cellular processes and networked devices. In these domains, the traditional contact temperature reading becomes inefficient, as the accuracy of a thermometer is limited by its size. Consequently, remote temperature readings have emerged to meet this need, where luminescence thermometry excels in the pursuit of highly sensitive and accurate thermometers. This field depends on temperature-induced changes in the spectroscopic properties of an ensemble of probes. However, thermal sensitivity may vary substantially depending on the chosen spectroscopic property. Therefore, this study aims to unify the traditional ratiometric approach and the thermal dependence of the emission lifetime to harvest higher sensitivities and lower uncertainties through dimensionality reduction. Accordingly, the principal component analysis (PCA) was employed, a technique often used for dimensionality reduction in machine learning. As a proof-of-concept, the SrY2O4:TbIII/IV(2at.%),EuIII(5at.%) phosphor was selected, synthesized by the Pechini modified method at 1100 °C/5 h under a partial CO atmosphere. Notably, the TbIII/IV was used as a co-dopant to distort the host lattice and amplify the intensity of EuIII emission bands because TbIV is spectroscopically inert in the visible region. The XPS analysis confirmed our hypothesis, revealing a 35/75% TbIII/TbIV ratio, being this small amount not detectable in the emission spectrum. To further avoid any TbIII emission, the sample was excited in the 5D2←7F0 (464 nm) EuIII 4f transition. Examining the emission spectrum of the phosphor, the characteristic 5D0→7F0-4 emission bands were detected, in addition to the 5D1→7F2 EuIII band (541 nm). The 5D0/5D1 pair's thermally coupled nature enabled the development of a ratiometric temperature probe, yielding a maximum relative sensitivity (Sr) of 0.95% K-1 in the 380-470 K range. By switching to the 5D0 lifetime using the 5D0→7F2 (612 nm) emission, and 5D2←7F0 (464 nm) excitation, maximum values of 0.42% K-1 for Sr were obtained in the same interval. Both values involve individual thermometric approaches, which raises the question of whether joining them would imply an improvement in sensitivity. In this sense, dual-parametric Sr was accomplished by PCA. The overall Sr values reached the 2.5% K-1 limit in the 350-460 K temperature range, representing a nearly 2.5-fold gain. Furthermore, a temperature uncertainty of 0.006 K was fostered when the dual-parametric approach was employed. Such low uncertainty allows accurate readouts at high temperatures. Hence, these outcomes demonstrate that enhanced sensitivities can be achieved through data analysis rather than solely relying on materials design.
Keywords: Data analysis, Dual-parametric thermal sensing, Dimensionality reduction
Acknowledgments: FAPESP 2023/05718-9 and CNPq 309448/2021-2.