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

Abstract

Lanthanide-doped upconversion (UC) nanomaterials with zero background auto-fluorescence are of extensive interest in optical fields. Here, a NaYF4:Yb3+/Er3+@Zr-UiO-66 nanostructure was prepared by simultaneously encapsulating NaYF4:Yb3+/Er3+ nanoparticles (NPs) and promoting the nucleation of UiO-66 under solvothermal condition. Traditional nanosize-surface induced defects and grain boundaries of NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) were greatly minimized; enabling a highly efficient energy transfer confirmed by the prolonged fluorescence lifetime and enhanced UC emission of NaYF4:Yb3+/Er3+@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 (Sr) were calculated to be 1.02 and 0.73% K−1 based on a pair of thermally coupled energy levels (TCLs) of (2H11/2 → 4I15/2, 4S3/2 → 4I15/2) and another pair of non-thermally coupled energy levels (NTCLs) of (2H11/2 → 4I15/2, 4F9/2 → 4I15/2), respectively. Besides, it exhibited effective internal optical heating property due to the thermal excitation between the two adjacent TCLs of 2H11/2 and 4S3/2 in NaYF4:Yb3+/Er3+ UCNPs as heated by increasing the laser power. This work demonstrates a feasible confined synthesis of NaYF4:Yb3+/Er3+@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.