Experimental and theoretical determination of the plasmonic responses and shape distribution of colloidal metallic...

The optical properties of gold and silver nanoparticles (NPs) dispersed in water and distributed in shape are investigated by introducing a shape distributed effective medium theory (SDEMT). This model takes into account the variation of depolarization parameter induced by a NP shape distribution. Simulations show that the shape distribution induces an inhomogeneous broadening and a decrease of the amplitude of the plasmon band. The number of plasmon bands and their positions depend on both the mean value of depolarization parameter and the NP material. By fitting the measured absorption spectra with the SDEMT, we unambiguously demonstrate that the depolarization parameter distribution, i.e., the shape distribution of nanoparticles can be deduced from absorption spectra.