High-Quantum-Efficiency Pr³⁺-Doped Li₇La₃Zr₂O₁₂ Garnet and Associated Temperature-Sensing Performance

The understanding of energy transfer mechanisms between different excited states of Pr³⁺ is closely bound up with exploiting high-quantum-efficiency Pr³⁺-doped luminescent thermometers and optimizing their temperature-sensing performances. Herein, we propose a new-type Pr³⁺-doped tetragonal-phase Li₇La₃Zr₂O₁₂ (Pr³⁺:LLZO) garnet luminescent thermometer and study accompanied photoluminescence (PL) properties. Combining composition optimization, we gain a fantastic room-temperature PL quantum efficiency within Pr³⁺:LLZO phosphors (77.48%), a value obviously superior to those of traditional Pr³⁺-doped garnet-type phosphors. The thermally induced fluorescence quenching of ³P₀ emissions within Pr³⁺:LLZO mainly originates from phonon-assisted thermal ionization, differing from the Pr³⁺-doped Y₃Al₅O₁₂ garnet. By contrast, the ¹D₂ case is akin to most Pr³⁺-doped materials in that the quenching behavior is seriously associated with the cross-relaxation between the ³P₀ and ¹D₂ states. On that basis, we propose a Pr³⁺:LLZO luminescence thermometry strategy by utilizing different quenching mechanisms of steady-state ³P₀ and ¹D₂ emissions, performing a comparable temperature-sensing capability to those Pr³⁺-based garnet-type luminescent thermometers. Our findings strengthen the importance of discerning the quenching mechanisms of Pr³⁺ emissions and provide a valuable perspective for designing high-quantum-efficiency Pr³⁺-doped garnet-type luminescent materials and relevant luminescence thermometry.