The gold core contributes a weak shoulder to the spectral response, visible near 520 nm. Compared to homometallic gold or silver, core-shell nanoparticles exhibit a broader range of extinction with the extinction intensity extending well into the red that would not normally be observed for isolated Ag NPs. Overall, the spectrum is not that of a mixture of separate Ag and Au NPs, nor is it the result of significant contributions from alloy formation .