A study was made of the defect structures and mechanism for the luminescence of non-doped, Tb3+-doped and Tb3+–Zn2+ co-doped alumina films treated at 300 to 800C. The electron paramagnetic resonance spectra observed before UV-irradiation were attributable to the non-bridging O radicals; Al–O–O. at 300 to 500C and Al–O. at 800C. The UV-light irradiation of the non-doped alumina films gave the electron paramagnetic resonance spectra with the 27Al hyperfine splitting. There exists a good correlation between the treatment temperature dependence upon the light-induced electron paramagnetic resonance signal intensity of the trapped electron and the nuclear magnetic resonance peak intensity due to the five-coordinated Al ion. It was concluded that the electron was captured at the O vacancy connected with the 5-coordinated Al. The broad electron paramagnetic resonance spectra due to the ground state of the Tb3+ ion were observed in the Tb3+-doped and Tb3+–Zn2+ co-doped alumina films. The Tb3+ concentration dependence of the electron paramagnetic resonance signal intensity due to the non-bridging Os suggested that Tb3+ prefers to form Al–O–Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced electron paramagnetic resonance signal of the electron trapped at O vacancy next the five-coordinated Al was also observed for the Tb3+–Zn2+ co-doped alumina film, which produced a long-lasting luminescence. The photo-generated trapped electron remained for several minutes under the room temperature. These experimental facts indicated that the five-coordinated Al ions act as the trapping sites to produce the long-lasting luminescence.

EPR Studies on Defects in Sol–Gel Derived Alumina Films. T.Ishizaka, S.Tero-Kubota, Y.Kurokawa, T.Ikoma: Journal of Physics and Chemistry of Solids, 2003, 64[5], 801-6