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⁺-O^2- 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.