Effective ratiometric optical thermometry based on inverse temperature dependent dual near infrared emission of Cr3+ doped BaAl4Sb2O12 phosphor

The device of reliable non-contact ratiometric optical thermometry technique gradually became a cutting-edge research pot over decades due to its intriguing features of rapid response, high accuracy and simple operation. In which, Boltzmann-based optical thermometry has attracted widespread attention for its exceptional reliability. Here in, we put forward an effective ratiometric optical thermometry based on the highly sensitive and effective Boltzmann-based ²E→ ⁴A ₂/ ⁴T ₂→ ⁴A ₂ emission ratio of BaAl _3.9Sb ₂O ₁₂:0.1Cr ³⁺. The phosphor shows dual near-infrared luminescence lines at 698 nm and 710 nm ( ²E→ ⁴A ₂) and the luminescence band near 750 nm ( ⁴T ₂→ ⁴A ₂). With the temperature elevating from 170 to 470 K, the emission intensity of luminescence lines undergoes continuous enhancement and possess excellent anti-thermal quenching property (3.5-fold at 470 K, compared to 170 K). In contrast, the emission intensity of luminescence band shows a monotonic decline trend. The luminescence intensity ratio shows a good linear relationship in the Arrhenius diagram, and the relative sensitivity reaches 2.08 % K ⁻¹ at 170 K, which corroborates the BaAl _3.9Sb ₂O ₁₂:0.1Cr ³⁺ has the potential as the optical cryogenic thermometer. In the end, the work provides some insights into the development of novel Cr ³⁺-doped thermometry materials based on the ²E and ⁴T ₂ energy level transitions in intermediate crystal field environments.