  We investigate the origin of the near-ultraviolet visible plasmonic
properties of three elemental materials from the p-block: Bi, Sb and Ga, with
the aim to achieve and exploit unconventional plasmonic effects beyond those
provided by noble metals. At such aim, we review and analyze a broad range of
optically-determined dielectric functions e of these elemental materials
available in the literature, covering a wide photon energy range (from 0.03 to
24 eV). It is shown that the contribution of Drude-like carriers to e1 (real
part of e) in the near-ultraviolet visible is negligible for Bi and Sb and
moderate for Ga. In contrast, the interband transitions of these elemental
materials show a high oscillator strength that yields a strong negative
contribution to e1 in the near-ultraviolet visible. Therefore in these
materials interband transitions are not a mere damping channel detrimental to
plasmonic properties. Remarkably, these interband transitions induce fully
(partially) the localized surface plasmon-like resonances taking place in Bi
and Sb (Ga) nanostructures in the near-ultraviolet visible. Plasmonic
properties achieved through interband transitions, without Drude-like carrier
excitation, are very attractive phenomena because they may give rise to a rich
and broad class of nanostructures and metamaterials in which plasmonic effects
will be tunable through the tailoring of band structure and by the occupancy of
electronic states.
