Multimodal Non-Contact Luminescence Thermometry with Cr-Doped Oxides

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).

A Theoretical Framework for Ratiometric Single Ion Luminescent Thermometers—Thermodynamic and Kinetic Guidelines for Optimized Performance

“…[ 258,259 ] The temperature dependence is the foundation of the lifetime‐based thermometric performance of Mn 4+ ‐ or Cr 3+ ‐activated phosphors at cryogenic temperatures due to the stronger electron‐phonon coupling in d orbitals. [ 63,70,72–75 ] Since coth( x ) → 1 for x ≫ 1 (), while coth( x ) ≫ 1 for x ≪ 1 (), the radiative decay rate becomes faster at low temperatures already.…”

“…If those states couple more strongly to local odd‐parity vibrational modes or phonons, the transition can become vibronically allowed. A very prominent example for that is the excited 2 E state (in cubically symmetric fields) of the 3d 3 configuration like in Mn 4+ or Cr 3+ , [ 64–77 ] but also the lowest excited (dominantly) triplet states 3 T 2u and 3 E u of the 4f 13 5d 1 configuration of Yb 2+ . [ 189 ]…”

Structurally induced tuning of the relative sensitivity of LaScO3:Cr3+ luminescent thermometers by co-doping lanthanide ions

“…In contrast to the 4f-4f transitions of the Ln 3+ ions, the spectroscopic properties of the TM ions such as emission and absorption wavelength are influenced by the locally surrounding ligand field of the ions This allows to optimize the thermometric performance of these luminescent ions and tailor it with respect to the practical requirements [14,[21][22][23][24][25][26][27][28][29][30][31][32]. This is especially well manifested in the case of Cr 3+ ions [22,27,28,[30][31][32][33]. The emission spectra of these ions can significantly differ in their appearance dependent on the crystal field strength.…”

From quencher to potent activator – Multimodal luminescence thermometry with Fe3+ in the oxides MAl4O7 (M = Ca, Sr, Ba)

“…Therefore, currently conducted works on TM-based luminescent thermometers aim at an enhancement of the emission intensity in the NIR range [12][13][14] . Among the most prominent candidates so far are the 3d 3 ions Cr 3+ and Mn 4+ doped into oxidic host compounds [15][16][17][18] . However, also several other TM ions show intense NIR luminescence with large a large response to small temperature changes [19][20][21][22][23][24][25][26][27][28] .…”