Photonic Artifacts in Ratiometric Luminescence Nanothermometry

Ongoing developments in science and technology requiretemperaturemeasurements at increasingly higher spatial resolutions. Nanocrystalswith temperature-sensitive luminescence are a popular thermometerfor these applications offering high precision and remote read-out.Here, we demonstrate that ratiometric luminescence thermometry experimentsmay suffer from systematic errors in nanostructured environments.We place lanthanide-based luminescent nanothermometers at controlleddistances of up to 600 nm from a Au surface. Although this geometrysupports no absorption or scattering resonances, distortion of theemission spectra of the thermometers due to the modified density ofoptical states results in temperature read-out errors of up to 250K. Our simple analytical model explains the effects of thermometeremission frequencies, experimental equipment, and sample propertieson the magnitude of the errors. We discuss the relevance of our findingsin several experimental scenarios. Such errors do not always occur,but they are expected in measurements near reflecting interfaces orscattering objects.