Hydrothermal chemistry, crystal structures, and spectroscopy of novel fluorides and borates

This dissertation is a two-part manuscript highlighting the utilities of the hydrothermal method for exploring phase space, then extending that to the targeted growth of potentially useful materials. Chapters 3 - 5 discuss the synthesis of Group 4 fluorides and oxyfluorides. The study of this class of compounds in regards to their single crystal structures is a rich, but neglected area. Among the Group 4 metals, compounds based on Zr and Ti have been extensively studied, while those based on Th and Hf are sparsely reported and those based on Ce(IV) are nearly completely neglected. Using the hydrothermal method, many new thorium, cerium(IV), and hafnium fluorides containing monovalent ions were synthesized and characterized. These systems exhibit great sensitivity toward both size and concentration of the monovalent metal in addition to experimental conditions such as temperature and reaction time. Interestingly, the descriptive and structural chemistries in the hafnium fluoride systems differ greatly from the thorium fluoride systems while showing no less structural variety. However, the structural chemistry in the cerium fluoride system acts as a bridge between thorium and hafnium fluoride systems. Crystal structures in these systems are introduced and discussed to describe the rich and varied chemistry. Several compounds exhibit luminescence from X-ray and UV-Vis excitations, and this interesting optical behavior is also discussed.;Chapters 6 and 7 focus on using the hydrothermal method to grow crystals having other sorts of optical functionality. A particularly rich system in this sense is the rare earth (RE) borate system, which can be useful for nonlinear optical (NLO), lasing, and scintillator applications. In particular, YBO 3 appears to be an especially versatile host, as it has an acentric crystal structure and can accommodate a wide range of rare earth dopants such as Nd(III), Er(III), and Yb(III), which can be used to generate lasing activity. Surprisingly, few single crystals of RE-doped YBO3 have been synthesized; in fact, recent work on RE-doped YBO3 powders has focused primarily on Eu(III). The absorption and emission spectra of the dopants in YBO 3 show a definitive blue-shift of up to 10 nm as compared to the commonly-used laser hosts of yttrium aluminum garnet (YAG) and YVO4, and initial findings show comparable emissions to that of RE-doped YAG and YVO4. Another group of acentric borates, Na3(RE)9O3(BO 3)8 (RE = Pr, Nd, Sm), were discovered in the process of synthesizing the RE-doped YBO3 compounds. Absorption/emission spectroscopy and lifetime measurements of these borates will also be discussed.