NIR to NIR luminescence thermometry in core/multishells-structured nanoparticles operating in the biological window

Abstract

Optical thermometry via near-infrared (NIR) emitting luminescent nanoparticles has attracted a great deal of attention during the last few years. In particular, nanothermometers operating in the biological windows are being strongly demanded for biomedical applications. In this sense, Tm3+ emissions centered around 800 and 1800 nm were explored here for ratiometric thermometry. And a luminescent thermometer based on NaYbF4/NaYF4: Tm3+-Yb3+/NaYF4 core/shell/shell-structured nanoparticles is designed. Excited by 980 nm laser, saturated emissions from Tm3+: 3H4→3H6 (~800 nm: first biological window NIR-I) and Tm3+: 3F4→3H6 (~1800 nm: third biological window NIR-III) transitions are readily obtained owing to the efficient upconversion processes in the core/multishells nanoparticles, finally resulting in the same dependence of NIR emissions on the pumping power. Different thermal response between 800 and 1800 nm emissions of Tm3+ ions enables optical thermometry via ratiometric method. In the physiological temperature range, the relative sensitivity Sr and absolute sensitivity Sa achieved here are about 0.33% K−1 and 3.9% K−1, respectively, with a temperature uncertainty of 0.75 K. These results illustrate that the nanothermometer developed in this work would be promising candidate for optical temperature measurement in bio-fields.