Rapid Room Temperature Synthesis and Temperature Sensitive Photoluminescence of Yb ³⁺ /Tm ³⁺ Co‐Doped K _0.3 Bi _0.7 F _2.4 Nanoparticles for Optical Thermometry

Abstract The study reveals that these nanoparticles exhibit highly tunable photoluminescence (PL), with distinct blue, red, and near‐infrared emissions that are highly sensitive to temperature changes. For the first time, the temperature‐dependent characteristics of PL emissions for optical thermometry behavior among 300–500 K for particular nanoparticles are also investigated. The temperature‐dependent fluorescence intensity ratio (FIR) technique, leveraging phonon‐mediated apparent temperature‐dependent coupling among Tm 3+ states, is employed to calculate the absolute sensitivity (S a ) and relative sensitivity (S r ) of particular nanoparticles. The results indicate high S a values of up to 0.0108 K −1 for sample A and 0.0017 K −1 for sample B across the given temperature range. Sample A exhibits a higher S r of 0.0122%K −1 at low temperatures, while decreasing to 0.0046%K −1 at higher temperatures, while sample B maintains a relatively consistent value over the same temperature range. These results highlight the potential of the synthesized nanoparticles as an effective optical thermometric probe. The Yb 3+ concentration directly modulates energy transfer efficiency and temperature sensitivity by influencing both the rate of energy transfer to Tm 3+ and the extent of nonradiative losses. Optimizing Yb 3+ content is thus crucial for achieving high sensitivity and stability in PL‐based optical thermometry, positioning Yb 3+ /Tm 3+ co‐doped K 0.3 Bi 0.7 F 2.4 nanoparticles as promising candidates for advanced noncontact temperature sensing applications.