Optical absorption properties of Au-Ag composite nanoparticles

Au-Ag composite nanoparticles were synthesized by simultaneously reduction of HAuCl₄ and AgNO₃ using NaHB₄ as reducing agent. The morphology and size of the particles were measured by the transmission electron microscopy (TEM). UV-vis absorption spectra results show that Au-Ag composite nanoparticles prepared by the one step co-reduction method have only one plasmon absorption band. The maximum absorption peak of Au-Ag composite nanoparticles between the absorption peaks of pure gold and pure silver nanoparticles and shift towards longer wavelength with increasing the molar ratio of Au and Ag ions in the reaction solution. The numerical analysis results based on the Mie scattering theory quantitatively account for the observed optical absorption properties dependence on the composition of Au-Ag composite nanoparticles.