Inherently Eu²⁺/Eu³⁺ Codoped Sc₂O₃ Nanoparticles as High-Performance Nanothermometers

Luminescent nanothermometers have shown competitive superiority for contactless and noninvasive temperature probing especially at the nanoscale. Herein, we report the inherently Eu²⁺/Eu³⁺ codoped Sc₂O₃ nanoparticles synthesized via a one-step and controllable thermolysis reaction where Eu³⁺ is in-situ reduced to Eu²⁺ by oleylamine. The stable luminescence emission of Eu³⁺ as internal standard and the sensitive response of Eu²⁺ emission to temperature as probe comprise a perfect ratiometric nanothermometer with wide-range temperature probing (77–267 K), high repeatability (>99.94%), and high relative sensitivity (3.06% K^–1 at 267 K). The in situ reduction of Eu³⁺ to Eu²⁺ ensures both uniform distribution in the crystal lattice and simultaneous response upon light excitation of Eu²⁺/Eu³⁺. To widen this concept, Tb³⁺ is codoped as additional internal reference for tunable temperature probing range.