Optical Thermometry Beyond the Diffraction Limit

From wide bandgap devices to lithium-ion batteries to emerging photocatalytic reactors, broad swaths of modern technology combine a need for nanoscale temperature measurements with challenging operating conditions such as large electromagnetic fields and ongoing chemical reactions. Far-field optical thermometry techniques are non-invasive and thus naturally well-suited to these challenging environments, but such measurements are inherently limited by optical diffraction. Here, we demonstrate two novel thermometry techniques that offer capabilities beyond those of traditional diffraction limited measurements, which are based on luminescent thermometers called upconverting nanoparticles (UCNPs). First, we demonstrate that heavily-doped UCNPs both display temperature-dependent emission that facilitates an approach known as ratiometric thermometry and enable a super-resolution imaging method called stimulated emission depletion (STED). The results indicate that temperature-dependent UCNP STED imaging has excellent potential for optical super-resolution thermometry of structures with nanoscale temperature heterogeneities. Second, we also demonstrate a dual-mode operando thermometry technique that enables simultaneous yet separate temperature and reaction monitoring during plasmonic photocatalysis. We apply this technique to 4 nitrothiophenol dimerization and record temperature rises exceeding 40 K, but complementary measurements rule out a purely thermal mechanism.
Andrea Pickel joined the Department of Mechanical Engineering at the University of Rochester as an Assistant Professor in July 2019. She received her Ph.D. in Mechanical Engineering from the University of California, Berkeley in May 2019, where she was supported by a National Science Foundation (NSF) Graduate Research Fellowship and a UC Berkeley Chancellor’s Fellowship. She received her B.S. in Mechanical Engineering with University and College Honors from Carnegie Mellon University in 2014. Her current research focuses on harnessing the unique properties of luminescent materials to develop nanothermometry techniques for challenging operating environments. Andrea is the recipient of an American Chemical Society Petroleum Research Fund (ACS PRF) Doctoral New Investigator Award (2020), a University of Rochester Furth Fund Award (2021), and an NSF CAREER Award (2022). Her teaching contributions have been recognized with the G. Graydon Curtis ’58 and Jane W. Curtis Award for Non-Tenured Faculty Teaching (2023).