ANISOTROPIC OPTICAL-SPECTRA OF ALPHA-AL2O3 SINGLE-CRYSTALS IN THE VACUUM ULTRAVIOLET REGION .2. SPECTRA OF OPTICAL-CONSTANTS

The spectra of optical constants of alpha-Al2O3 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 [c] and normal to it. The optical constants include the complex i ndex of refraction, conductivity, complex dielectric constant, loss fu nctions and effective number of electrons per unit cell. The spectra i n E less than or similar to 78 eV are interpreted in terms of the inte rband transitions from the O 2p and 2s bands to the Al conduction band s and the free electron-like absorption of photons by the 0 2p band el ectrons. The volume energy loss function has a prominent peak at E is similar to 26.4 eV for the plasma oscillation dominantly of the 2 p el ectrons. The spectral features in E greater than or similar to 78 eV r esulting from electronic transitions from the Al L2,3 levels are prese nted with the L2,3 exciton doublet, e.g., at 78.72 eV and 79.15 eV for epsilon2//.