Study of blue photoluminescence in titanium doped Al2O 3 Single-Crystals

Abstract

Optical properties have been investigated in titanium doped sapphire, prepared under oxidized condition. Charge-transfer transitions to 3d states of tetravalent Ti4+ from 2p ones of O2- are found to be located below the fundamental absorption edge of Al2O3. The photo-excitation for this band leads to the intense blue emission, the spectrum of which is quite different from the luminescence of the d-d transitions in trivalent Ti3+. The UV-irradiation also leads to an absorption peak below the charge-transfer band, resulted from that the photo-excited electrons in part form color centers. The post-annealing at higher temperatures above 300°C completely destroys the color centers. The blue photoluminescence is found to be greatly suppressed by the UV-irradiation and is recovered by the post-annealing. This fact indicates that the color centers prevent the blue emission. © 2011 Ceramic Society of Japan.