Modulation of Localized Surface Plasmon Resonance of Nanostructured Gold Crystals by Tuning Their Tip Curvature with Assistance of Iodide and Silver(I) Ions

Abstract

In this article, we describe a series of experiments that systematically addressed and clarified the effects of iodide, silver ions, and ascorbic acid (AA) concentration on the morphology of gold nanorods (Au NRs) during the overgrowth process. When iodide ions, silver ions, or both were present in the growth solution, a morphology of Au nanocrystals ranging from thick NRs, cuboidal shaped NRs, dogbone-like NRs, to dumbbell NRs, respectively, was obtained. The appearance of the third peak in the UV−vis spectra indicates the formation of lobes on the tips of Au NRs. In addition, when different seeds (such as Au NRs of short aspect ratio and spherical Au nanocrystals) whose {111} facets were covered by iodide ions were used, horns of different length on Au seeds were formed. Taken together, the results mentioned above and cross section change of the tips of Au NRs, two lobes instead of four formed on each tip of the Au NRs are explained for the first time, and their growth from {111} facets is assisted by the formation of AgI, which can catalytically reduce Au ions into atoms on those facets. The optical spectra of nanostructured Au crystals can be tuned from 520 to 955 nm by controlling their tip curvature or platinum coating. A wide color gamut can be readily obtained by using a random dispersion of nanostructured Au NR-based crystals.