From Deep Cryogenics to Extreme Heat: Unlocking Single-Ion Luminescent Thermometry with Pr³⁺-Activated Ca₃Sc₂Si₃O₁₂ and Ca₃Sc₂Ge₃O₁₂ Garnets

High Resolution Image Download MS PowerPoint Slide Luminescence thermometry is gaining prominence as a noncontact-reading temperature sensing technique, offering high precision, robustness, and material tunability. In this work, we report Pr 3+ -doped garnets, Ca 3 Sc 2 Si 3 O 12:0.1% Pr and Ca 3 Sc 2 Ge 3 O 12:0.1% Pr, as promising candidates for wide-range optical thermometry based on both emission intensity and decay time metrics. The silicate garnet exhibits a record operational range of 25–1225 K, with relative thermal sensitivity spanning 0.5–1.3%·K –1 over 250–1225 K, sustained by intense and thermally controlled 4f 1 5d 1 → 4f 2 emission. Temperature-dependent luminescence measurements reveal a continuous and monotonic decrease in both emission intensity and lifetime, supporting two-modal reliable, quantitative thermal readout. At elevated temperatures (≥900 K), thermally stimulated back-transfer from the 1 D 2 to the 3 P 0 level activates an additional 3 P 0 / 1 D 2 intensity ratio metric, achieving 0.44%·K –1 sensitivity. The germanate counterpart shows strong performance in the 20–225 K range, with relative sensitivities exceeding 5%·K –1 . These Pr 3+ -activated phosphors, featuring submicron particle size, phase stability, and broad thermal response, enable multimodal, single-ion thermometry across a continuous, ultrawide temperature span. These findings highlight the potential of garnet hosts for next-generation luminescent thermometers in high-demand environments such as catalysis, aerospace, nuclear monitoring, and space exploration.