Mapping Elevated Temperatures with a Micrometer Resolution Using the Luminescence of Chemically Stable Upconversion Nanoparticles.

The temperature-sensitive luminescence of nanoparticles enables their application as remote thermometers. The size of these nanothermometers makes them ideal to map temperatures with a high spatial resolution. However, high spatial resolution mapping of temperatures >373 K has remained challenging. Here, we realize nanothermometry with high spatial resolutions at elevated temperatures using chemically stable upconversion nanoparticles and confocal microscopy. We test this method on a microelectromechanical heater and study the temperature homogeneity. Our experiments reveal distortions in the luminescence spectra that are intrinsic to high-resolution measurements of samples with nanoscale photonic inhomogeneities. In particular, the spectra are affected by the high-power excitation as well as by scattering and reflection of the emitted light. The latter effect has an increasing impact at elevated temperatures. We present a procedure to correct these distortions. As a result, we extend the range of high-resolution nanothermometry beyond 500 K with a precision of 1-4 K. This work will improve the accuracy of nanothermometry not only in micro- and nanoelectronics but also in other fields with photonically inhomogeneous substrates.
Competing Interests: The authors declare the following competing financial interest(s): T.v.O., R.G.S., and H.H.P.G. work for DENSsolutions B.V., a company manufacturing and marketing in situ TEM systems. The remaining authors declare no competing interests.
(© 2021 The Authors. Published by American Chemical Society.)