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Title: Bifunctional Luminescent Thermometer-Manometer Based on Cr³⁺–Cr³⁺ Pair Emission

Authors: M. Szymczak, A. Antuzevics, P. Rodionovs, M. Runowski, U. R. Rodríguez-Mendoza, D. Szymanski, V. Kinzhybalo, L. Marciniak

Journal: ACS Applied Materials & Interfaces

DOI: 10.1021/acsami.4c11806

In this study, Prof. Marciniak's group and collaborators investigated the potential of leveraging the thermal and pressure-dependent spectroscopic properties of Cr³⁺ ions and Cr³⁺-Cr³⁺ pairs for luminescence thermometry and manometry. Using CaAl₁₂O₁₉:Cr³⁺, in which three distinct crystallographic sites can be occupied by Cr³⁺ ions, it was possible to simultaneously observe the ²E→⁴A₂ and ⁴T₂→⁴A₂ luminescence of Cr³⁺ ions, as well as the ⁴A₂,⁴T₂→⁴A₂,⁴A₂ emission band of Cr³⁺-Cr³⁺ pairs. High-pressure experiments revealed unusual behavior of Cr³⁺ ions in this host material. Specifically, the spectral position of the ⁴A₂,⁴T₂→⁴A₂,⁴A₂ band of Cr³⁺-Cr³⁺ pairs exhibited minimal sensitivity to pressure changes up to 7 GPa. In contrast, the ²E→⁴A₂ band of Cr³⁺ ions displayed a monotonic spectral shift with increasing pressure, what can be attributed to changes in the covalency of the Cr³⁺-O^2- bond. As a result, the luminescence intensity ratio (LIR) between these two spectral ranges showed a monotonic dependence on pressure, achieving a maximum relative sensitivity of 70% GPa^-1 at 0.05 GPa. Notably, the proposed LIR demonstrated minimal temperature sensitivity, with a TIMF parameter of 150 K GPa^-1. Additionally, the thermal population of the ⁴T₂ level of Cr³⁺ ions resulted in a gradual increase in the intensity of this band with rising temperature. The inverse thermal monotonicity of this band relative to the ²E→⁴A₂ band enabled the development of a ratiometric luminescence thermometer with a sensitivity of 1% K^-1 at 180 K. This work represents the first luminescent manometer based on the luminescence of Cr³⁺-Cr³⁺ pairs, highlighting the potential of such systems for advanced pressure and temperature sensing applications.

This work was funded by the NCN Opus project UMO-2020/37/B/ST5/00164. The work presented was funded under the NCN Opus project UMO- 2022/45/B/ST5/01629.