Abstract
Luminescence methods for non-contact temperature monitoring have evolved through improvements of hardware and sensor materials. Future advances in this field rely on the development of multimodal sensing capabilities of temperature probes and extend the temperature range across which they operate. The family of Cr-doped oxides appears particularly promising and we review their luminescence characteristics in light of their application in non-contact measurements of temperature over the 5–300 K range. Multimodal sensing utilizes the intensity ratio of emission lines, their wavelength shift, and the scintillation decay time constant. We carried out systematic studies of the temperature-induced changes in the luminescence of the Cr3+-doped oxides Al2O3, Ga2O3, Y3Al5O12, and YAlO3. The mechanism responsible for the temperature-dependent luminescence characteristic is discussed in terms of relevant models. It is shown that the thermally-induced processes of particle exchange, governing the dynamics of Cr3+ ion excited state populations, require low activation energy. This then translates into tangible changes of a luminescence parameter with temperature. We compare different schemes of temperature sensing and demonstrate that Ga2O3-Cr is a promising material for non-contact measurements at cryogenic temperatures. A temperature resolution better than ±1 K can be achieved by monitoring the luminescence intensity ratio (40–140 K) and decay time constant (80–300 K range).
Highlights
Luminescence thermometry is a non-contact temperature measurement technique that utilizes emission characteristics that exhibit a temperature dependence [1]
Among many materials used for non-contact luminescence thermometry, Cr3+ -doped compounds are interesting since luminescence of Cr3+ exhibits a variety of temperature-dependent effects
The relative this, we developed a phenomenological model that can provide an interpretation for the variety of decrease of the decay time constant at low temperatures accounts for ca. 5%, which is τ = f(T)
Summary
Luminescence thermometry is a non-contact temperature measurement technique that utilizes emission characteristics that exhibit a temperature dependence [1]. Application in the low-temperature range focuses the search onto systems with thermally induced processes, where processes of reorganization of population of excited states and thermal quenching require a low activation energy This can translate into changes of a luminescence parameter with temperature, as observed for the luminescence lifetime in tungstates and molybdates [37], intensity ratio of emission lines in rare earth RE3+ doped Y2 O3 [21], or emission line shift in Ga-doped ZnO [38]. Among many materials used for non-contact luminescence thermometry, Cr3+ -doped compounds are interesting since luminescence of Cr3+ exhibits a variety of temperature-dependent effects The reason for this is due to the energy structure of the Cr3+. These transitions give rise to two sharp emission lines, R1 (E→4 A2 ) and R2 (2A→4 A2 ), observed in the deep red spectral range with the exact wavelength being material-dependent [39]
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