Adverse Role of Shape and Size in Second-Harmonic Scattering from Gold Nanoprisms

Gold nanoparticles are widely used in different fields. They are currently under extensive investigation with regard to their linear and nonlinear optical properties. So far, nanoparticles with centrosymmetrical shapes, such as nanospheres or nanorods, have received the main attention. In this work, the properties of gold nanoprisms exhibiting a highly noncentrosymmetrical threefold symmetry are investigated with hyper-Rayleigh scattering (HRS). Aqueous solutions of gold nanospheres and nanoprisms with different sizes were synthesized. The first hyperpolarizability magnitudes of both the nanospheres and nanoprisms were determined separately with the assumption of a surface origin of the nonlinearity. Using polarization-resolved HRS, retardation is shown to be largely underdeveloped for the nanoprisms as opposed to the nanospheres. The nanoprism shape noncentrosymmetry has therefore a leading role in the HRS response although it is also shown that surface defects induce deviations from the ideal threefold symmetry.