2D Thermal Maps Using Hyperspectral Scanning of Single Upconverting Microcrystals: Experimental Artifacts and Image Processing

Abstract

Whereas lanthanide-based upconverting particles are promising candidates for several micro- and nanothermometry applications, understanding spatially varying effects related to their internal dynamics and interactions with the environment near the surface remains challenging. To separate the bulk from the surface response, this work proposes and performs hyperspectral sample-scanning experiments to obtain spatially resolved thermometric measurements on single microparticles of NaYF4: Yb3+,Er3+. Our results showed that the particle’s thermometric response depends on the excitation laser incidence position, which may directly affect the temperature readout. Furthermore, it was noticed that even minor temperature changes (<1 K) caused by room temperature variations at the spectrometer CCD sensor used to record the luminescence signal may significantly modify the measurements. This work also provides some suggestions for building 2D thermal maps that shall be helpful for understanding surface-related effects in micro- and nanothermometers using hyperspectral techniques. Therefore, the results presented herein may impact applications of lanthanide-based nanothermometers, as in the understanding of energy-transfer processes inside systems such as nanoelectronic devices or living cells.

Correction Due to Nonthermally Coupled Emission Bands and Its Implications on the Performance of Y2O3:Yb3+ /Er3+ Single-Particle Thermometers

“…Realize that the integral on the denominator in eq includes the complete 4 S 3/2 band. If one does not remove the 2 H 9/2 → 4 I 13/2 band from the spectrum, the thermometric parameter R would have a power dependence which tends to decrease with the increase of the excitation power, as shown by Rühl et al and also discussed in a recent work from our group Pessoa et al The source of the higher uncertainty in the uncorrected case is exactly this undesired power-dependence of the LIR. Since we are performing single particle measurements, it is experimentally challenging to keep the excitation conditions exactly the same over the time.…”

“…In a previous work from our group using NaYF 4 :Yb 3+ /Er 3+ microcrystals, the effect of the three-photon band correction was critical when imaging the luminescence emission spatially resolved inside a single microparticle. In that case, we limited the integration interval of the 4 S 3/2 band to a wavelength lower than the beginning of the overlapping.…”

“…Practically, there is almost no variation on S r between the corrected and uncorrected cases, but a key reduction is achieved in the temperature readout uncertainty δ T from 0.6 to 0.3 K. This is calculated by uncertainty propagation based on the correlated fitting parameters Δ E eff and C eff for each case. Further details on the error calculation procedure can be found in refs , , and .…”

“…Since we are performing single particle measurements, it is experimentally challenging to keep the excitation conditions exactly the same over the time. There is always some nanometric mechanical movement, for example, that slightly shifts the focal position (due to the room temperature variation, for instance). As a result, the excitation power is critical in this case, and its variation increases considerably the measurement uncertainty.…”

“…Besides this, Ln 3+ systems are well-known also for their relatively high upconversion (UC) efficiency . However, to achieve higher spatial resolutions in thermometry experiments, the single-particle measurement level must be accomplished, and a thorough investigation of Ln 3+ systems in this regime is under current discussion in the literature. − …”