Sc3+-induced double optimization strategies for boosting NIR-II luminescence and improving thermometer performance in CaF2: Nd3+, Nd3+/Yb3+@NaYF4 nanocrystals

Lanthanide-based near-infrared-emitting nanocrystals have aroused enormous attention for their promising applications in biomedical imaging and temperature sensing. However, the concentration quenching effect and energy migration to surface quenchers are inevitable parts of the lanthanide doped systems, which cause a low signal-to-noise ratio of detection. Herein, we delicately design CaF2: Nd3+/Sc3+@NaYF4 nanocrystal, in which the Sc3+ ions are introduced to block the cross relaxation between adjacent Nd3+ ions, and the buffer layer of NaYF4 can suppress surface defects, resulting in 10-fold higher photoluminescence at 1060 nm compared to CaF2: Nd3+ nanocrystal under 808 nm excitation. Besides, CaF2: Nd3+/Yb3+ as a ratiometric luminescence nanoprobe is optimized through additional Sc3+ to enhance emission intensity and tune thermal sensitivity, which allows precise detection of temperature. This work not only provides a feasible strategy to design efficient near-infrared-emitting lanthanide nanocrystals, but also opens up enormous potential of high-sensitivity ratiometric nanothermometers in nanomedicine.