Anisotropic Optical Spectra of α-Al 2O 3 Single Crystals in the Vacuum Ultraviolet Region. II. Spectra of Optical Constants

The spectra of optical constants of α-Al 2 O 3 single crystals at 297 K and 10 K are presented over the range of photon energies from 6 eV to 120 eV for the electric fields of incident light parallel to optic axis and normal to it. The optical constants include the complex index of refraction, conductivity, complex dielectric constant, loss functions and effective number of electrons per unit cell. The spectra in E ≥ 78 eV are interpreted in terms of the interband transitions from the O 2p and 2s bands to the Al conduction bands and the free electron-like absorption of photons by the O 2p band electrons. The volume energy loss function has a prominent peak at E ∼26.4 eV for the plasma oscillation dominantly of the 2p electrons. The spectral features in E ≤78 eV resulting from electronic transitions from the Al L 2,3 levels are presented with the L 2,3 exciton doublet, e.g. , at 78.72 eV and 79.15 eV for e 2// .