Ultraviolet–visible absorption spectra of the colloidal metallic elements

TLDR

Ultraviolet–visible absorption spectra of 10 nm colloidal particles for 52 metallic elements were calculated using Mie theory from their optical constants. The study systematically investigates how the spectra of colloidal particles change when the particle shape is varied from spherical to spheroidal in the dipole approximation. This is done by generating contour plots of the absorbance cross‑section versus the real and imaginary parts of the dielectric function, and the approach is also applied to hollow spherical particles. The spectra cover 200–900 nm, with well‑resolved bands for Sc, Ti, V, Y, Cd, Eu, Yb, Hg, Th, Cu, Ag, Au and s‑block metals, while most others exhibit only continuous visible absorption rising to broad UV bands near 200 nm; the data suggest Ca, Sr, Ba, Eu, Yb, Th and possibly Sc, Ti, V, and Y may be promising for surface‑enhanced Raman scattering.

Abstract

The ultraviolet–visible absorption spectra are given for 10 nm diameter colloidal particles of 52 of the metallic elements, calculated from the optical constants of the metals by means of Mie theory. For most of the elements the spectra cover the range 200–900 nm. Well resolved absorption bands are observed for colloidal Sc, Ti, V, Y, Cd, Eu, Yb, Hg and Th as well as for colloids of Cu, Ag, Au and the s-block metals. However, for the majority of the colloidal metallic elements in this size range there is only a continuous absorption in the visible range, rising to broad and poorly resolved absorption bands in the ultraviolet near 200 nm. The difference in the way that the spectra of colloidal particles of different metals change when the particle shape is varied from spherical to spheroidal is investigated systematically in the dipole approximation. This is achieved by means of contour plots of the absorbance cross-section for the particles vs. the real and imaginary parts of the dielectric function for the metals, and this method of investigation is extended also to hollow spherical particles. The results suggest that Ca, Sr, Ba, Eu, Yb, Th and possibly Sc, Ti, V and Y may merit experimental investigation as new metals for exhibiting surface-enhanced Raman scattering.