Nanoscale Ultrasensitive Temperature Sensing Based on Upconversion Nanoparticles with Lattice Self-Adaptation.

Upconversion nanoparticles have recently received increasing attention due to their outstanding performance in temperature sensing at the nanoscale. Although much effort has been devoted to improve their thermal sensitivity, there is no efficient way for achieving significant enhancement. Here, we show that lattice self-adaptation can unlock a new route for remarkably enhancing the thermal sensitivity of upconversion nanoparticles. The thermally sensitive fluorescence intensity ratio (FIR) of the dopant Er3+ is used for indicating the temperature variation, while a heterojunction of NaGdF4/NaYF4 is prepared as host material to produce a lattice distortion at the interface which is also sensitive to temperature. With the increase of temperature, the FIR of the transitions 2H11/2/4S3/2 → 4I15/2 increases, accompanied by the self-adapted decrease of interface lattice distortion that leads to the additional increase in FIR. Using core/shell upconversion nanoparticles with lattice self-adaptation, we achieve an enhanced thermal sensitivity three times higher than core-only nanoparticles.