Boltzmann Thermometry in Cr³⁺‐Doped Ga₂O₃ Polymorphs: The Structure Matters!

Abstract

The performance of luminescent Cr3+‐doped thermometers is strongly influenced by the locally surrounding ligand field. A universal relationship between the thermometric performance and structural/chemical parameters is highly desirable to drive the development of effective Cr3+‐based thermal sensors avoiding trial‐and‐error procedures. In this view, as prototypes, the electronic structure and the thermometric performance of Cr3+‐doped α‐Ga2O3 and β‐Ga2O3 polymorphs are compared. Combining a detailed theoretical and spectroscopic investigation, the electronic configuration and the crystal field (CF) acting on the Cr3+ in α‐Ga2O3 are described for the first time and compared with β‐Ga2O3:Cr3+ polymorph to discuss the thermometric behavior. A linear relationship between the 4T2–2E energy gap (directly linked to the relative sensitivity) and the CF strength Dq is demonstrated for a wide variety of materials. This trend can be considered as a first step to set guiding principles to design effective Cr3+‐based Boltzmann thermometers. In addition, as a proof of concept, particles of β‐Ga2O3:Cr3+ thermometer are used to locally measure in operando thermal variations of Pt catalysts on β‐Ga2O3:Cr3+ support during a catalytic reaction of C2H4 hydrogenation in a contactless and reliable mode, demonstrating their real potentials.

One ion to catch them all: Targeted high-precision Boltzmann thermometry over a wide temperature range with Gd3+

“…With the spectroscopic value of ∆ E CF = 72 cm −1 , the expected onset temperature for Boltzmann thermalization between the two excited levels is thus approximately 23 K, very close to the observed deviation from Boltzmann behaviour below 25 K. A similar deviation has also been observed in the case of Cr 3+ 67 , 78 , which can be explained by the same kinetic effect. In turn, the optimum temperature range for the most precise thermometry that exploits this energy gap between the two Kramers’ doublets of the 6 P 7/2 level of Gd 3+ is between 30 and 51 K according to Eq.…”

Wide Dynamic Range Thermometer Based on Luminescent Optical Cavities in Ga2O3:Cr Nanowires

“…[5] Taking this into account, several sensor platforms for optical thermometers have been recently attempted attending to specific underlying mechanisms, such as luminescence ratiometric or interferometry properties. [6][7][8][9][10] Luminescent thermometers offer a variety of spectral features, as intensity of emission bands, bandwidth, emission ratio between different lines, spectral shift, or lifetime, which are affected by temperature-dependent mechanisms and hence can be used as quantitative observable parameters to be translated into a temperature value. [3] In this sense, up-conversion nanoparticles and quantum dots are taking the lead in the luminescent thermometry scenario offering reliable performances.…”

Rationalizing the Thermal Response of Dual‐Center Molecular Thermometers: The Example of an Eu/Tb Coordination Complex

“…[1,3,[34][35][36][37] This popular concept (known as luminescence intensity ratio thermometry, LIR) is described by the simple Boltzmann's law, [38,39] allowing to overcome some of the limitations affecting the performance of luminescent thermometers based on a single emission. [1,3,35] By far, thermometers based on trivalent lanthanide ions (Ln 3+ ) [1,35,[40][41][42][43][44] (including materials co-doped with Ln 3+ ions and transition metals [45,46] ) have popularized the LIR thermometry concept.Ratiometric luminescent thermometers can be classified in single-ion (encompassing crossover- [47] and Boltzmann-based…”