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, that were irradiated at room temperature using a Febetron 706 variable energy pulsed-electron-beam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ∼100 nm) bands centred around 380, 425, and 445 nm for CaTiO3, SrTiO3 and BaTiO3, respectively. These emission bands are similar to cathodoluminescence emissions from 25 keV electron irradiation attributed by others to direct conduction-valence band transitions in unreduced samples and oxygen vacancies in reduced samples. CaTiO3, SrTiO3 and BaTiO3 all have emission thresholds of 0.26±0.02 MeV. This corresponds to a threshold displacement energy for oxygen, Ed of 45±4 eV.