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

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 alpha-Ga2O3 and beta-Ga2O3 polymorphs are compared. Combining a detailed theoretical and spectroscopic investigation, the electronic configuration and the crystal field (CF) acting on the Cr3+ in alpha-Ga2O3 are described for the first time and compared with beta-Ga2O3:Cr3+ polymorph to discuss the thermometric behavior. A linear relationship between the T-4(2)-E-2 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 beta-Ga2O3:Cr3+ thermometer are used to locally measure in operando thermal variations of Pt catalysts on beta-Ga2O3:Cr3+ support during a catalytic reaction of C2H4 hydrogenation in a contactless and reliable mode, demonstrating their real potentials.

Automated summary

The electronic structures and thermometric performances of Cr3+-doped alpha-Ga2O3 and beta-Ga2O3 polymorphs were compared, revealing a linear relationship between the T-4(2)-E-2 energy gap and the CF strength Dq. This trend could provide guiding principles for designing effective Cr3+-based Boltzmann thermometers. Additionally, beta-Ga2O3:Cr3+ particles were demonstrated to locally measure thermal variations during a catalytic reaction, showcasing their potential for real-world applications.