Nanocomposites of Au Nanorods and Core–Shell NaGdF4:Yb3+,Er3+@NaYF4 Upconversion Nanoparticles for Temperature Sensing

Here, we report a nanocomposite with excellent photothermal performance promising for photothermal treatment. This nanocomposite is prepared by linking Au nanorods (NRs) to NaGdF4:18% Yb3+, 2%Er3+@NaYF4 core–shell upconversion nanoparticles (UCNPs) with bridging of polyethylene glycol molecules. Solutions with the composite nanoparticles can be heated by the irradiation of a near-infrared 980 nm laser, and the photothermal effect in terms of temperature rise can reach 21.3 °C with excitation power density as low as 0.090 W/cm2. This highly effective photothermal performance is attributed to coincidence of the emission band of the UCNPs and the absorption band of the Au NRs, which facilitates the light-to-heat conversion. The structure of the composite and the concentration of the Au NRs in the solution are also optimized through the emission intensity, green-to-red intensity ratio, and the photothermal effect in this work. Compared with previous research studies, the strength in the lower irradiation power density makes the nanocomposite promising for further photothermal treatment and temperature sensing.