Suchergebnisse

Luminescence thermometry is used in a variety of research fields for noninvasive temperature sensing. Lanthanide‐doped micro‐/nanocrystals are exceptionally suitable for this. The popular concept of luminescence‐intensity‐ratio thermometry is based on emission from thermally coupled levels in a single lanthanide ion, following Boltzmann's law. These thermometers can measure temperature with low uncertainty, but only in a limited temperature range. In this work, a Ho3+‐based thermometer is presented and quantitatively modeled with sustained low temperature uncertainty from room temperature up to 873 K. The thermometer shows bright green and red luminescence with a strong and opposite dependence on temperature and Ho3+ concentration. This is the result of temperature‐dependent competition between multi‐phonon relaxation and energy transfer, feeding the green‐ and red‐emitting levels, respectively, following excitation with blue light. This simple and quantitative model of this competition predicts the output spectrum over a wide range of temperatures (300–873 K) and Ho3+ concentrations (0.1–30%). The optimum Ho3+ concentration can thus be determined for reliable measurements over any temperature range of interest. Quantitative modeling as presented here is crucial to optimally benefit from the potential of energy‐transfer thermometers to achieve low measurement uncertainties over a wide temperature range. ; This project has received funding from the European Union's Horizon 2020 FET Open programme under grant agreement No 801305 (NanoTBTech).

Water phase transition divides the areas of soil approximation from the point of view of its elastic properties. It is interesting to study changing of acoustic characteristics, both kinematic and dynamic, in the process of freezing and thawing, since they can be indicators of various inelastic characteristics of the transition from one state to another. In the article we present results of initial stage of research on the topic identified in the title. This includes: design of a measuring cell that introduces minimal distortions in ultrasonic p and s waves measurements on water-saturates ground sample, monitoring sample temperature, performing ultrasonic measurements with a time step that provides necessary detailing for observing time and temperature dependencies of the waves characteristics registered during the phase transition data analisys.

In this article we discuss the results of ultrasonic measurements using p and s waves on a sample of full water–saturated sand in the temperature range –20 ᵒC — + 20 ᵒC. The results are: dependence of kinematic and dynamic parameters of the ultrasonic signal on temperature and elastic waves attenuation parameter. We propose method to calculate the attenuation parameter of p and s waves at ultrasonic frequencies for a wide temperature range. The values of the attenuation parameter at negative and positive temperatures differ by 40–50 times for p waves and by 2 orders of magnitude for s waves. A smooth change in the attenuation parameter from –5 ᵒC (–10 C) to 0 ᵒC for p (s) waves was observed. The attenuation affecting the dynamic parameters reacts faster to the thawing of frozen ground than the waves velocity, which is most relevant in the case of plastic–frozen rocks and at temperatures close to 0.