Optical Spectra of Rare Earth Activated BaTiO3

Abstract

BaTiO3 has been activated with Pr, Sm, Eu, Dy, or Er ions. The fluorescence spectra were determined at —196°C, —28°C, room temperature, and at 130°C. We looked for crystalline field effects on the energy levels of the rare earths and changes in these effects as the crystallographic phase of BaTiO3 is changed. In particular, we sought changes at the Curie point in going from the ferroelectric tetragonal phase to the cubic phase. The high-temperature data were largely unresolvable and no changes were observed at the low-temperature transitions in going from the tetragonal to the orthorhombic phase in the range of 5 to 13°C and from the orthorhombic to the rhombohedral phase in the range of —70 to —80°C. No crystal field splittings were observed at any temperature, leading to the possible conclusion that the rare earth centers are in positions of either high symmetry or low field strength. The fluorescence data support the hypothesis that the rare earths are present as the trivalent ions and that they can be assigned energy levels and term signatures resulting from the 4fn configuration.