Size- and Wavelength-Selective\nOptical Heating in\nMie-Resonant Silicon Nanospheres for Nanothermometry and Photothermal\nApplications

The photothermal heating properties of perfectly spherical\ncrystalline\nsilicon nanoparticles having Mie resonances in the visible range are\nstudied under different illumination wavelengths by using the Raman\nscattering peak as a nanothermometer. Analytical calculations reveal\nthat the magnetic quadrupole (MQ) Mie mode is the most suitable mode\nfor photothermal heating. The experimentally obtained size and illumination\nwavelength dependence of the temperature rise agrees quantitatively\nwith numerical simulations, and the heating efficiency reaches up\nto 381 K/(mW/μm<sup>2</sup>) when the illumination wavelength\nof 633 nm matches the MQ resonance. Conversely, tuning the illumination\nwavelength to a relatively nonabsorbing mode, such as the electric\ndipole (ED) mode, can significantly reduce the heating effect. In\nthis context, the ED mode functions as a practically heating-less\nnanoantenna, promoting the surface-enhanced fluorescence of nearby\ndye molecules, while high-<i>Q</i> modes, e.g., MQ and electric\nquadrupole (EQ) modes, serve as an optical heating platform. Furthermore,\nthe photothermal heating and Raman thermometry of silicon nanoparticles\nin water and in cancer cells are demonstrated.