The defect chemistry of erbium-doped strontium titanate

The purpose of this dissertation was to determine the defect chemistry of strontium titanate as reflected through the optical spectroscopy of erbium dopants. Erbium ions substitute at strontium positions and act as donor dopants. The various erbium sites were resolved through site-selective spectroscopy and associated with the Ruddlesden-Popper shear phases of strontium titanate. One erbium site apiece was found for strontium titanate's {dollar}rm Srsb2TiOsb4{dollar} and {dollar}rm Srsb3Tisb2Osb7{dollar} phases. Four sites were attributed to the SrTiO{dollar}sb3{dollar} phase.; The two sites within the paraelectric SrTiO{dollar}sb3{dollar} phase reflected ionic and electronic defects. The local symmetry about the two sites was determined by the multiplicity of erbium site spectra when the SrTiO{dollar}sb3{dollar} phase was in its cubic phase. The sites arbitrarily named 1A and 1B were found to be distantly- and locally-compensated, respectively. The lattice's displacive phase transition caused the 1A site to undergo a dynamic Jahn-Teller distortion. At 10 Kelvin, the 1B site could be resolved into three sub-sites, which is consistent with local compensation by strontium vacancies.; The erbium site distribution was monitored as a function of the sample's preparation. The site distribution as a function of sample stoichiometry was not consistent with a random distribution of compensating defects but rather the formation of titanium-rich shear phases formed by the aggregation of strontium vacancies.; Electronic defects were also evidenced through emission spectroscopy and electron paramagnetic resonance. Previously characterized self-trapped excitons could be excited with sub-band gap excitation and transferred energy to the rare earth ions. The growth and depletion of self-trapped excitons with time and light could be monitored through changes in upconverted rare earth emission. When the electronic defects were present in high concentration, the 1A and 1B sites did not reflect the lattice's phase transition 100K below its onset. With the depletion of the electronic defects, the 1A and 1B sites reflect the lattice's phase transition within 10K of its onset.