Local- and distant-charge compensation of Eu3+ ions in defect centers of SrTiO3.

Abstract

Site-selective spectroscopy of rare-earth-doped materials has proven to be a powerful method for investigating solid-state defect chemistry at the atomic level. In this paper, the spectral transitions of single-crystal and polycrystalline samples of ${\mathrm{SrTiO}}_{3}$:${\mathrm{Eu}}^{3+}$ are sorted by site-selective laser spectroscopy into the major and minor sites that are found in this perovskite-structure material. The major site is shown to have crystal-field multiplicities, relative fluorescence and absorption intensities, level lifetimes, and level degeneracies that are consistent with the tetragonal symmetry associated with a distantly-charge-compensated center. The electronic and vibronic levels for all the visible transitions are determined for this center. These levels exhibit temperature-dependent splittings and shifting that reflects the cubic-tetragonal phase transition that occurs at 106 K. In addition, there are eleven other centers that are assigned to centers with local compensation by vacancies or electronic defects. Electronic defects are also evident from the photobleaching and photoinduced darkening that is also observed in these samples. These effects are observed in both single-crystal and polycrystalline samples, although the linewidths and line shapes of the polycrystalline samples are shown to be dependent on the preparation conditions.