Optical emission due to ionic displacements in alkaline earth titanates

Optical emission spectra in the 300-700 nm range were collected from single crystal CaTiO3, SrTiO3 and BaTiO3, and polycrystalline CaTiO3 samples, tha t were irradiated at room temperature using a Febetron 706 variable energy pulsed-electron-beam generator. The long-lived emissions (up to microsecond s after the electron pulse) consist of broad (halfwidths similar to 100 nm) bands centred around 380, 425, and 445 nm for CaTiO3, SrTiO3 and BaTiO3, r espectively. These emission bands are similar to cathodoluminescence emissi ons from 25 keV electron irradiation attributed by others to direct conduct ion-valence band transitions in unreduced samples and oxygen Vacancies in r educed samples. CaTiO3, SrTiO3 and BaTiO3 all have emission thresholds of 0 .26 +/- 0.02 MeV. This corresponds to a threshold displacement energy for o xygen, E-d of 45 +/- 4 eV. (C) 2001 Elsevier Science B.V. All rights reserv ed.