Photonic Artifacts in Ratiometric Luminescence Nanothermometry

Abstract

Ongoing developments in science and technology require temperature measurements at increasingly higher spatial resolutions. Nanocrystals with temperature-sensitive luminescence are a popular thermometer for these applications offering high precision and remote read-out. Here, we demonstrate that ratiometric luminescence thermometry experiments may suffer from systematic errors in nanostructured environments. We place lanthanide-based luminescent nanothermometers at controlled distances of up to 600 nm from a Au surface. Although this geometry supports no absorption or scattering resonances, distortion of the emission spectra of the thermometers due to the modified density of optical states results in temperature read-out errors of up to 250 K. Our simple analytical model explains the effects of thermometer emission frequencies, experimental equipment, and sample properties on the magnitude of the errors. We discuss the relevance of our findings in several experimental scenarios. Such errors do not always occur, but they are expected in measurements near reflecting interfaces or scattering objects.

Mapping Temperature Heterogeneities during Catalytic CO2 Methanation with Operando Luminescence Thermometry

“…As random photon-counting noise or reaction-induced heating cannot explain the variations in apparent temperature under inert conditions, we propose different possible origins: spatial variations in (1) absorption, (2) scattering of thermometer emission by the sample, or (3) background fluorescence. Local variations in absorption and/or scattering at the wavelengths monitored to determine I 1 and I 2 would lead to deviations of the recorded LIR from the emitted LIR . Moreover, the fluorescence background from the sample could add to I 1 and I 2 and therefore affect the LIR.…”

Er3+-Doped Upconversion Nanoparticle Coatings for Thermometric Microscanning: Tackling Experimental Factors

“…It is important to mention that in all cases, the particles were in direct contact with the materials in question. This not only ensures efficient heat transfer but also minimizes distortions in the emission spectra, and therefore in the thermal readings, because of the modified local density of optical states (LDOS) near dielectric or metallic surfaces …”

“…A drop of m-UCNPs was deposited by drop-casting on the device covering all tracks homogeneously. Note that the metallic tracks are covered by a PI film tens of microns thick, i.e., the UCNPs are separated from the metallic tracks by a distance several times larger than the emission wavelength, so the modified LDOS should not affect the emission spectra . Then, a DC voltage of 7 V was applied to produce heating.…”

“…In addition, knowledge of potential artifacts and systematic error sources is critical. Regarding UCNPs-based thermometry, several challenges have been identified, such as addressing optical interference on metallic surfaces, , and controlling the intensity of the excitation light to prevent undesired optical transitions. , …”

Luminescence Thermometry Beyond the Biological Realm

“…This approach, known as “ratiometric” thermometry, is the most common UCNP thermometry method. Ratiometric sensing is advantageous over approaches based on absolute intensities since ratiometric signals are often insensitive to intensity variations resulting from sample absorption and scattering and day-to-day alignment variations, for example, although recent work discussed further in Section (Measurement Artifacts) has demonstrated that parameters including the excitation laser intensity and surrounding environment can affect UCNP ratiometric thermometry signals under certain circumstances and caution must be taken. − Ratiometric thermometry traditionally requires calibration using a temperature-controlled platform combined with a reference temperature probe, meaning that these approaches are by definition secondary thermometry methods. However, strategies for applying UCNPs for primary thermometry, in which temperature can be determined directly from a known physical law with no required calibration, have also been reported …”