Crystals are the heart of the development of advance technology. Their existence is the essential foundation in the electronic field and without it there would be little to no progress in a variety of industries including the military, medical, and technology fields. The discovery of a variety of new materials with unique properties has contributed significantly to the rapidly advancing solid state laser field. Progress in the crystal growth methods has allowed the growth of crystals once plagued by difficulties as well as the growth of materials that generate coherent light in spectral regions where efficient laser sources are unavailable. The collaborative progress warrants the growth of new materials for new applications in the deep UV region. This work involves the use of hydrothermal crystal growth for exploring the descriptive chemistry of various metal borate systems in which several new structures were isolated. Conventional melt-based crystal growth methods can be problematic in synthesizing metal borates due to incongruent melting as well as the typical viscous nature of the borate flux melts. This can lead to glassy products making it difficult to grow optical quality metal borate single crystals. Due to these difficulties, other synthetic methods such as hydrothermal crystal growth for these types of materials are explored. The motivation for the exploratory research of this system derives from the commercially important &beta&ndashBaB2O4 and LiB3O5. Both materials have excellent properties however; generation of coherent light below 225 nm is inefficient due to low transmittance in the deep UV region. Similarly, several other known metal borates have good optical properties but they all have limitations. For example, beryllium containing borate KBe2BO3F2 (KBBF) have been of interest in the recent years because it generates coherent light in the deep UV region; however, a problem exists with the layered structure preventing high quality crystals from forming. Hydrothermal technique has proven to be an attractive alternative crystal growth method, especially with the growth of good quality KBBF crystals. This dissertation explores the descriptive crystal chemistry of hydrated alkali and alkaline earth borate systems in an attempt to grow &beta&ndashBaB2O4 or similar analogs. In an effort to improve the thermal properties of hydrated borates, this work was also extended to systematically introduce more stable anions and oxyanions into the borate lattice. Furthermore, preliminary photoluminescence of europium doped borate and borosilicate structures give information about their optical properties and potential applications. The work with europium led to a new rich class of europium silicates and borosilicates in which several new structures were uncovered. The formation of these new materials demonstrates the versatility of the crystal chemistry of metal borates under hydrothermal conditions
