Optical Spectra of Y3Al5O12(YAG) Single Crystals in the Vacuum Ultraviolet Region

Optical absorptions in the tail region and the reflectivity at room temperature in the VUV region up to ∼40 eV are measured for YAG single crystals. Various optical constants are derived therefrom as functions of photon energy by means of the Kramers-Kronig relation. The Urbach rule parameters are determined experimentally for the tails intrinsic to YAG single crystals. The exciton peak is inferred to lie near the photon energy of the convergence point (7.012 eV) of the Urbach tails, taking into account the peak position (∼7.0 eV) of the excitation spectrum of Ce 3+ -emission from YAG:Ce 3+ phosphors. A tentative interpretation of the spectral features found in the spectra of optical constants in terms of the energy levels of the constituent free ions is given.