Structural investigations of ytterbium dopant sites and elpasolite nanocrystal structure

Abstract

The relationship between molecular and materials structure and observed properties is a pillar of chemistry and materials science. Understanding the structural character of materials at both the bulk and nanoscale is critical for establishing these relationships, and often requires non-traditional techniques to properly elucidate microstructure and local behavior. This isespecially true in the perovskites and elpasolites, which exhibit a wide array of interesting optical, electronic, and magnetic properties, all of which are fine-tunable by minor changes to structure or the addition of dopants. This dissertation describes my research in three studies using X-ray total scattering, pair distribution function analysis, X-ray absorption, and transmission electron microscopy to understand the local structure of lanthanide dopants in cesium lead chloride perovskites and chromium trihalides, and determine the crystal structure and stability of a new iodide elpasolite nanocrystal. These various projects highlight the importance of local structure in leading to the unique optical and magnetic properties of ytterbium-doped cesium lead chloride and chromium trihalides, and the ability of surface free energy to stabilize structures at the nanoscale which are unstable in the bulk. Together these results expand our understanding of the structural origins of optical, magnetic, and stability properties of these energy-relevant materials.