Dual-Mode Optical Thermometry Design in Lu₃Al₅O₁₂:Ce³⁺/Mn⁴⁺ Phosphor

There is a challenge for noncontact temperature-sensing techniques and the related materials, in which a highly reliable contactless thermometer probe with low cost and high sensitivity is in demand. Here, the Lu₃Al₅O₁₂:Ce³⁺/Mn⁴⁺ phosphor has been designed and prepared for the high-performance fluorescence temperature-sensing application in a novel one-pot, self-redox, solid-state process. Benefiting from the different electron-lattice/phonon interactions of Ce³⁺ and Mn⁴⁺, two distinguishable emission peaks with significantly different temperature responses originating from Ce³⁺ and Mn⁴⁺ are realized. Applying the fluorescence intensity ratio of Mn⁴⁺ versus Ce³⁺ and the decay lifetime of Mn⁴⁺ emission as the temperature readout, a dual-mode optical temperature-sensing mechanism was proposed and studied in the temperature range of 100-350 K. The maximum relative sensitivities (S_r) are derived as 4.37 and 3.22% K^-1 respectively, as well as a large chromaticity shift visible to naked eyes (ΔE = 153 × 10^-3 in 100-350 K) is observed. This is the first report of a Ce³⁺,Mn⁴⁺ co-doped dual-emitting phosphor, and its unique optical thermometric features demonstrate the high potential of Lu₃Al₅O₁₂:Ce³⁺/Mn⁴⁺ as an accurate and reliable thermometer probe candidate.