Synthesis and Applications of Lanthanide Sulfides and Oxides

The chemistry of the lanthanide and actinide elements remains the last great frontier of the periodic table. While many main group and transition metal elements have been known from antiquity, it was not until the late 20 th century that the lanthanides found ready industrial and commercial applications as phosphors, optical coatings, polishing agents, and catalytic applications. This dissertation focuses on two of the key fields where lanthanides find ready application: as optically active materials with a focus on the lanthanide sulfides, and as catalytic materials with a focus on cerium oxide. The lanthanide sulfides have attracted considerable interest for their potential as solar energy conversion materials, pigments, infrared window materials, and phosphor host media. All of these properties stem from their semiconducting properties with useable band gaps ranging from 2.7 to 0 eV. However, applications of these materials remain limited due to their synthetic difficulty along with their not well understood properties compounded by both their difficulty in manufacturing as well as in simulating largely due to the need to take into account f-shell electrons. This dissertation presents the fundamental band properties of lanthanum, gadolinium, and samarium sulfides as well as a rapid chemical vapor deposition method for the synthesis of highly textured samarium sulfide thin films. Even more than the sulfides, the lanthanide oxides have attracted tremendous interest from industry and academia for their use as phosphors and catalytic applications, most notably cerium oxide in automotive three-way catalysts and in the petroleum industry as a cracking catalyst. In contrast to the lanthanide sulfides, the syntheses of the oxides are rapid and inexpensive causing many of the oxides to find ready applications even though the complexities of their chemistries are not yet well understood. This dissertation presents the fundamental kinetics and mechanism investigations for cerium oxide (ceria) as it is used for catalyzing the direct synthesis of organic carbonates from CO 2 and methanol. This reaction is of particular interest due to its slow kinetics allowing for fundamental investigations, while ready industrial demand for organic carbonates and CO 2 utilization mean that this chemistry may find ready application. Even more so, I would like to thank my advisor Dr. Chin Li " Barry " Cheung for his training, guidance, and especially his patience, which has enabled me to complete my doctoral studies at the University of Nebraska-Lincoln. His perseverance, support, and unwavering curiosity have provided me with the opportunities …