Optical interband structure and the low energy plasmon in ScH2

The optical absorptivity of ScH2 has been measured at 4.2 K between 0.1 and 4.4 eV, and the dielectric functions determined through Kramers-Kronig analysis. The low energy optical features are shown to be dominated by free-electron-like absorption and a screened plasmon at 1.47 eV. The presence of the low energy plasmon explains the deep blue appearance in ScH2 and the lanthanide dihydrides. Interband absorption is shown to be dominant above about 1.5eV. 8author)