In-situ confinement of ultra-small NaYF4:Yb3+/Er3+ UCNPs as multifunctional ratiometric thermometer and optical heater

Lanthanide-doped upconversion (UC) nanomaterials with zero background auto-fluorescence are of extensive interest in optical fields. Here, a NaYF 4 :Yb 3+ /Er 3+ @Zr-UiO-66 nanostructure was prepared by simultaneously encapsulating NaYF 4 :Yb 3+ /Er 3+ nanoparticles (NPs) and promoting the nucleation of UiO-66 under solvothermal condition. Traditional nanosize-surface induced defects and grain boundaries of NaYF 4 :Yb 3+ /Er 3+ upconversion nanoparticles (UCNPs) were greatly minimized; enabling a highly efficient energy transfer confirmed by the prolonged fluorescence lifetime and enhanced UC emission of NaYF 4 :Yb 3+ /Er 3+ @Zr-UiO-66 nanocomposite. The optical thermometry property of nanocomposite was investigated based on the fluorescence intensity ratio (FIR) technique in the temperature range of 303–393 K. The maximum relative temperature sensitivities (S r ) were calculated to be 1.02 and 0.73% K −1 based on a pair of thermally coupled energy levels (TCLs) of ( 2 H 11/2  →  4 I 15/2 , 4 S 3/2  →  4 I 15/2 ) and another pair of non-thermally coupled energy levels (NTCLs) of ( 2 H 11/2  →  4 I 15/2 , 4 F 9/2  →  4 I 15/2 ), respectively. Besides, it exhibited effective internal optical heating property due to the thermal excitation between the two adjacent TCLs of 2 H 11/2 and 4 S 3/2 in NaYF 4 :Yb 3+ /Er 3+ UCNPs as heated by increasing the laser power. This work demonstrates a feasible confined synthesis of NaYF 4 :Yb 3+ /Er 3+ @Zr-UiO-66 nanocomposite with extreme UC emitting performance, and it holds great potential acting as both ratiometric thermometer and optical heater for multifunctional applications.