Gallium Phosphide Nanoparticles for Low-Loss Nanoantennas in Visible Range

Colloidal nanoparticles of gallium phosphide (GaP) with moderately high refractive index (n > 3) and a small extinction coefficient in the visible range are developed using a combination of mechanical milling and a pulsed laser melting process in solution. The combined process yields GaP nanoparticles with an almost spherical shape and the smooth surface. The single particle scattering spectroscopy reveals that smoothening of the surface by the pulsed laser melting process is crucial for achieving distinctive Mie resonances of the dipolar and higher-order modes in the visible range. The near-field profile at the Mie resonances studied by electron energy loss spectroscopy in a scanning transmission electron microscope confirms the existence of the magnetic dipole mode. Finally, the Purcell enhancement of fluorescence of molecules on the surface due to the Mie resonances is demonstrated.