| Technology is an important part of society today and research in new single crystals is important for the advancement of solid-state optics. Progress in medical and military fields is due to the progress with crystal chemistry. Discovering new materials that have interesting optical properties can create advancement in optics. Fluoride materials are documented to have much longer excited state lifetimes than oxide materials but are not widely used as many are of undesirable quality for optics. The long excited state lifetimes of fluorides can lead to interesting properties such as upconversion, which allows for conversion to UV or visible wavelengths, and this warrants the exploratory chemistry of the rare-earth fluorides.;This dissertation explores the hydrothermal growth of rare-earth fluoride materials. Melt based methods are more conventional, and fluoride materials have been grown in this way but are of poor quality and their crystal structures are not well understood. In many cases problems exist with incongruent melting with the conventional melt based techniques. The hydrothermal method was implemented in order to produce high quality, single crystal structures. As a result of this, new synthetic routes to known phases and novel materials were discovered.;The commercially available fluoride material, LiYF4, motivated this research; although it is available, it is not as widely used as its oxide counterparts, such as YAG and sapphire. Hydrothermal synthesis was conducted on this material and its lutetium counterpart LiLuF4. Using small alkali metals, materials were synthesized of the form AREF4, where A = Li+ and Na +, RE = Y3+, Er3+, and Lu3+. These materials have a potential for disorder within the structure as seen in the NaErF4 structure. Substituting for larger alkali metals produced different phases, such as ARE2F7, where A = K+, Cs+, and Rb+, RE = Y3+, La3+-Lu 3+, and ARE3F10, where A = K+ and Rb+, RE = Y 3+, Lu3+, Sm3+, Gd3+. These ARE2F7 phases have a complex crystal structure that is dependent on the growth technique. Although the structure of the ARE3F10 materials is already known, new materials were synthesized in order to expand the phase space. Adding additional alkali metals into these types of materials produced two novel crystal structures, LiKREF5, where RE = Lu3+, Tm 3+, and Yb3+, and LiNaLu2F8. High-pressure crystallography was conducted on the thulium compound of LiKREF 5 in order to determine any phase changes under pressure. In addition to these more complex structure types, the simple REF3 materials were also synthesized, where RE = La3+-Lu3+. Understanding the chemistry of these materials can allow for more targeted synthesis of desired materials. Spectroscopy of these materials shows typical emissions for a variety of applications. |
