Defect Aggregation Kinetics in Calcium Fluoride

Defects in solid materials are responsible for many of their most interesting and critical properties. We have developed a site-selective laser technique that allows us to monitor the aggregation of rare earth ion defects in solids on the microscopic scale. This Excitation-Absorption laser method enables us to derive kinetic rate information and thermodynamic parameters for the distribution of defects in solids. For doped materials, various types of defects arise when the dopant ions have ionic charges that differ from the charges of host crystal ions. In model systems such as alkaline earth fluorides doped with trivalent rare earth ions, some defect sites consist of a single dopant ion, while others consist of clusters of dopant cations and interstitial anions. Heat treatment of doped samples leads to a distribution of the various types of defect sites that is characteristic of the temperature and length of heat treatment and the total dopant ion concentration. The results from a study of the formation of trivalent europium ion defect aggregates in calcium fluoride indicate that our method successfully monitors changes in individual site concentrations resulting from heat treatment. The results of this study are consistent with the formation of negatively-charged dimer and trimer defects in Eu ^{3+}:CaF_2 crystals from isolated europium ion and (Eu:F_ {rm i}) single pair defects. In addition, we present evidence for rapid equilibrium between the isolated ion and the single pair. Other work presented in this thesis includes the development of a high-temperature fluorine oxidation apparatus that we used to convert divalent europium ions to the trivalent state in calcium fluoride single crystals. This apparatus was also used to increase the superconducting T _{rm c}'s of YBa _2Cu_3O_ {rm 7-x} through modification of the copper-oxygen oxidation states.