Authors: K.B. Mogensen, K. Kneipp
Affilation: Technical University of Denmark, Denmark
Pages: 431 - 434
Keywords: plasmon band, blueshift, size dependence, aqueous phase
In this work, we report the size-dependent blue shift of the silver nanoparticle (AgNP with radius R) plasmon band in aqueous solution by means of UV/VIS spectroscopy. An oxidative dissolution scheme using cyanide in the solution allows a gradual decrease in the particle sizes by oxidation during recording of the optical spectra. A 1/R-dependence of the plasmon peak energy as well as a saturation of the maximum energy is observed. Cyanide is chosen for dissolution, because it is a very strong nucleophile, meaning that it has a strong ability to donate negative charge density to the silver. It forms a coordinative bond by donation of an electron pair, which generates a screening layer around the NPs. The free electrons of the NPs thereby shift towards the center, which increases the average electron density. This results in a blueshift of the plasmon band, which is in accordance with a simple Drude model of the dielectric function. These measurements are complementary to recent electron energy loss spectroscopy (EELS) studies of the plasmon band blueshift, however with a much higher energy resolution.