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

Pressure dependence of spectral positions of the 2E → 4A2 and 4T2 → 4A2 bands of Cr3+ ions, resulting from changes in Cr3+–O2– covalency and variations in crystal field strength, respectively, is commonly utilized in luminescence manometry. However, as demonstrated in this paper, the luminescence of Cr3+–Cr3+ pairs shows insensitivity to pressure changes, making this signal suitable as a luminescence reference. The significant difference in the thermal and pressure dependences of luminescence with Cr3+ occupying different crystallographic positions in CaAl12O19:Cr3+ enables the development of a dual-function luminescence thermometer that operates in both ratiometric and lifetime-based readout modes. The presented first demonstration on utilization of Cr3+–Cr3+ pairs luminescence for sensing applications may rekindle interest in Cr3+–Cr3+ pairs for the development of optical sensors for physical quantities.