Synthesis, structure and luminescence studies of europium alkoxides and related complexes

Europium is an important component in many solid-state phosphor materials due to its spectral transitions at wavelengths well suited to the human eye. Europium-containing solid state-materials would be improved through better control of particle size and homogeneity by using well-defined europium alkoxide complexes via sol-gel or MOCVD processing, but little is known about the synthesis of the necessary europium alkoxide complexes. Heterometallic europium alkoxide complexes would be especially useful as single-source precursors for multi-component phosphor materials. This dissertation describes the development of synthetic procedures to obtain europium alkoxide complexes, the investigation of structural features of these complexes, and luminescence studies to probe the utility of europium alkoxide complexes as solution-based models for europium phosphors. Europium metal dissolves in liquid ammonia and this solution reacts with 2,6-disubstituted-aryl-alcohols to form mono-, bi- and tetrametallic europium aryloxide complexes, depending on the substitution of the aryl alcohol. Reactions involving mixtures of europium and alkaline earth metals were found to produce mixtures of homometallic aryloxide products. Reactions of europium with the chelating alcohols 2-methoxyethanol and carbitol produce highly aggregated and very soluble europium alkoxide complexes, which form crystalline adducts when treated with aryl alcohols. In the case of 2-methoxyethanol the alcohol adducts react with Al₂Me ₆ to form aluminum-containing heterometallic species. The reaction of europium metal with isopropanol and aryl alcohols provides a route to tri-, penta-, octa-, and nonametallic europium species, which contain divalent and/or trivalent europium, depending on the reaction conditions. Similar reactions run with mixtures of europium and barium yielded heterometallic alkoxide complexes. Well-characterized heterometallic europium/zirconium halide complexes have also been synthesized by using the di-zirconium-nona-isopropoxide (dzni) unit as an ancillary ligand for the lanthanides. The conversion of dzni lanthanide halides to cyclopentadienyl complexes is also described. The synthesis of anhydrous hexafluoroacetylacetonate and pentafluorobenzoate complexes of europium from europium oxide and metal is described. Luminescence spectra and structures of the new compounds are discussed in the appropriate chapters.