Synthesis of NIR-II fluorescent ratio-metric thermometers via the integration of lanthanide-doped nanoparticles and quantum dots

Fluorescent ratio-based thermometers, especially the combination of thermal sensitive quantum dots (QDs) with thermal stable lanthanide doped nanoparticles (NPs), have demonstrated great potential for temperature sensing due to their high relative thermal sensitivity. In this work, we synthesized NaYF 4 : 3%Nd@NaYF 4 @SiO 2 @Ag 2 S nanocomposites (NCs), where Ag 2 S QDs were integrated onto the surface of NaYF 4 : 3%Nd@NaYF 4 NPs. Under 808 nm excitation, the luminescence intensity ratio of the NCs in the 1200 nm and 1060 nm exhibits a strong linear relationship with temperature. The NCs show a relative sensitivity of 5.05% °C -1 at 47 °C and maintain photostability through six temperature cycles, under various pH conditions, and during prolonged irradiation. In vitro fluorescence imaging further confirms their potential for temperature measurement in aqueous environments. This approach offers a novel design concept for the creation of a highly sensitive nanothermometer.