Photochemical Synthesis of Monodisperse Size-Controlled Silver Decahedral Nanoparticles and Their Remarkable Optical Properties

Monodisperse decahedral silver nanoparticles have been synthesized with excellent shape selectivity (>99%) by novel photochemical transformation of aqueous silver nanoparticle precursors. The procedure employs intense white light and is very robust and reproducible. The precursor solution transforms from a mixture of shapes dominated by small silver platelets into the decahedra, driven by superior stability of decahedral seeds. The decahedra size can be varied by adjusting intensity and spectral properties of the irradiating light. Furthermore, the decahedra can be controllably photochemically regrown to larger sizes, while fully preserving the monodispersity. Silver decahedra exhibit remarkable optical properties featuring a bicolored appearance due to the interplay between plasmonic adsorption and scattering. The sharp plasmon resonances of silver decahedra were tunable from 455 to 570 nm through size variation. Finally, silver decahedra exhibited greatly superior enhancement of Raman scattering compared to other silver nanoparticles. Overall, our findings highlight the importance of pentagonal symmetry in metal nanoparticles and offer a powerful general approach to monodisperse shapes via selective regrowth of appropriately identified and stabilized intermediates.