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

Luminescence thermometry is gaining prominence as a noncontact-reading temperature sensing technique, offering high precision, robustness, and material tunability. In this work, we report Pr³⁺-doped garnets, Ca₃Sc₂Si₃O₁₂:0.1% Pr and Ca₃Sc₂Ge₃O₁₂:0.1% 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 4f¹5d¹ → 4f² 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 ¹D₂ to the ³P₀ level activates an additional ³P₀/¹D₂ 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 Pr³⁺-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.