Bi₂₄Al₂O₃₉:Mn⁵⁺-phosphor-based single-emission ratiometric thermometer.

This article focuses on the development and characterization of near-infrared (NIR) luminescent thermometers based on Mn⁵⁺-doped Bi₂₄Al₂O₃₉ phosphors. Using a single-emission luminescence intensity ratio (LIR) technique, which is insensitive to excitation fluctuations and optical dispersion, the study demonstrates temperature sensing from 300 to 380 K with maximal relative sensitivities of 3.54% K⁻¹ in the physiological range (300–330 K) and 3.98% K⁻¹ at 351 K under 970 nm excitation. The Bi₂₄Al₂O₃₉:0.5%Mn⁵⁺ phosphor synthesized via a high-temperature solid-state method exhibits strong NIR excitation and emission, making it a promising candidate for biological temperature sensing applications. The research highlights the advantages of Mn⁵⁺-based NIR thermometers over other luminescent materials due to their thermal stability, low toxicity, and compatibility with the optical window of biological tissues.