Bifunctional Luminescent\nThermometer-Manometer Based\non Cr<sup>3+</sup>–Cr<sup>3+</sup> Pair Emission

Pressure dependence of spectral positions of the <sup>2</sup>E\n→ <sup>4</sup>A<sub>2</sub> and <sup>4</sup>T<sub>2</sub> → <sup>4</sup>A<sub>2</sub> bands of Cr<sup>3+</sup> ions, resulting from\nchanges in Cr<sup>3+</sup>–O<sup>2–</sup> covalency\nand variations in crystal field strength, respectively, is commonly\nutilized in luminescence manometry. However, as demonstrated in this\npaper, the luminescence of Cr<sup>3+</sup>–Cr<sup>3+</sup> pairs\nshows insensitivity to pressure changes, making this signal suitable\nas a luminescence reference. The significant difference in the thermal\nand pressure dependences of luminescence with Cr<sup>3+</sup> occupying\ndifferent crystallographic positions in CaAl<sub>12</sub>O<sub>19</sub>:Cr<sup>3+</sup> enables the development of a dual-function luminescence\nthermometer that operates in both ratiometric and lifetime-based readout\nmodes. The presented first demonstration on utilization of Cr<sup>3+</sup>–Cr<sup>3+</sup> pairs luminescence for sensing applications\nmay rekindle interest in Cr<sup>3+</sup>–Cr<sup>3+</sup> pairs\nfor the development of optical sensors for physical quantities.