Abstract
Lanthanide-based luminescent nanothermometers play a crucial role in optical temperature determination. However, because of the strong thermal quenching of the luminescence, as well as the deterioration of their sensitivity and resolution with temperature elevation, they can operate in a relatively low-temperature range, usually from cryogenic to ≈800 K. In this work, we show how to overcome these limitations and monitor very high-temperature values, with high sensitivity (≈2.1% K–1) and good thermal resolution (≈1.4 K) at around 1000 K. As an optical probe of temperature, we chose upconverting Yb3+–Tm3+ codoped YVO4 nanoparticles. For ratiometric sensing in the low-temperature range, we used the relative intensities of the Tm3+ emissions associated with the 3F2,3 and 3H4 thermally coupled levels, that is, 3F2,3 → 3H6/3H4 → 3H6 (700/800 nm) band intensity ratio. In order to improve sensitivity and resolution in the high-temperature range, we used the 940/800 nm band intensity ratio of the nonthermally coupled levels of Yb3+ (2F5/2 → 2F7/2) and Tm3+ (3H4 → 3H6). These NIR bands are very intense, even at extreme temperature values, and their intensity ratio changes significantly, allowing accurate temperature sensing with high thermal and spatial resolutions. The results presented in this work may be particularly important for industrial applications, such as metallurgy, catalysis, high-temperature synthesis, materials processing and engineering, and so forth, which require rapid, contactless temperature monitoring at extreme conditions.
Highlights
Temperature is a crucial parameter for most of industrial processes, like sintering, formation of metal alloys, catalytic reactions, formation of new materials under extreme conditions, and so forth
Its rapid, accurate, and online monitoring is a challenging task for many specialists working in various fields of science, industrial researchers, and material engineers.[1−6] For these purposes, various luminescence thermometry techniques have been proposed, developed, and applied.[7−18] in general, because the luminescence of materials is significantly quenched at increasing temperature, these optical methods are usually limited to low- and mild-temperature (≈400−800 K) ranges.[19−22]
This is because they allow high-spatial resolution of temperature sensing, as well as they do not need a high-energy excitation source, which can cause other undesired effects, such as uncontrolled polymerization during catalytic processes or additional heating.[1,27,48−50] It is worth noting about novel application of lanthanide-based luminescent thermometers in optical vacuum sensing, that is, conversion of luminescent thermometers into low-pressure sensors, utilizing the effect of laserinduced heating of the materials, which is enhanced under vacuum conditions.[27,51]
Summary
Temperature is a crucial parameter for most of industrial processes, like sintering, formation of metal alloys, catalytic reactions, formation of new materials under extreme conditions, and so forth. By the use of the band intensity ratio associated with non-TCLs of Yb3+ and Tm3+ ions (940/800 nm), we have achieved unprecedentedly high sensitivity (2.1% K−1) and temperature resolution (1.4 K) at extreme temperature values
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