Plasmon resonance and raman modes in Pb nanoparticles obtained in extract of Opuntia ficus-indica plant

Colloidal nanoparticles were obtained by green synthesis, embedded in the Opuntia ficus-indica plant extract. Optical measurements allowed us to detect two absorption bands centered in 230 nm and 298 nm. Agglomerates of Pb nanoparticles have size in the range 2-8 nm. The effective absorption cross section of spherical Pb nanoparticles was calculated by applying the Mie theory for colloidal systems and compared to optical absorption measurements of Pb nanoparticles. The Raman spectrum of the samples after the reduction of Pb, shows a band at low wavenumbers centered at 116 cm^-1. Similar bands have been assigned to small Pb and Ag clusters in other experimental results. Additionally, we used the density functional theory (DFT) as well as semi-empirical methods to assign this band to radial breathing modes of Pb metal nanoparticles.