Upconversion Luminescence Enhancement through Crystal Field Engineering for Multimode Optical Thermometry with High...

Noncontact optical thermometry based on intense upconversion (UC) luminescence holds significant promise for biomedical applications. In this study, Y³⁺ doping is employed to tailor the local crystal field environment of LaScO₃:Yb³⁺/Er³⁺, achieving a 2.7-fold enhancement in the UC luminescence intensity. Rietveld structural refinement and Eu³⁺ spectral probing confirm that this enhancement stems from Y³⁺-induced lattice distortion, which disrupts the local symmetry around the luminescent centers. The optimal doping concentrations of Yb³⁺, Er³⁺, and Y³⁺ are determined to be 5%, 2%, and 10%, respectively. Moreover, the UC luminescence mechanisms are further elucidated in detail by analyzing the spectral results. Based on the thermally coupled levels and Stark sublevels of Er³⁺, three fluorescence intensity ratio (FIR)-based thermometers are constructed in green, red, and near-infrared (NIR) regions, all revealing high thermometric sensitivity and accuracy. Crucially, the present NIR thermometer enables temperature detection through 8 mm of biological tissue with a negligible FIR deviation, showcasing its exceptional potential for deep-tissue thermal sensing. This work provides a strategic pathway for developing efficient UC materials and advanced optical thermometers for biological applications.