Abstract: BiI3 has been investigated for its unique properties as a layered compound semiconductor for many decades. Among these are several qualities that make it an attractive candidate for a room temperature gamma ray sensor. However, despite the exceptional atomic, physical, and electronic properties of this material, good resolution gamma ray spectra had never been reported for BiI3. The shortcomings that have previously prevented BiI3 from reaching success as a gamma ray sensor are herein identified and suppressed to unlock the performance of this promising compound. Included in this work are studies on a number of methods which have, for the first time, enabled BiI3 to exhibit spectral performance rivaling many other candidate semiconductors for room temperature gamma ray sensors. New approaches to crystal growth are explored that allow BiI3 spectrometers to be fabricated with up to 2.2% spectral resolution at 662 keV. Fundamental studies on trap states, dopant incorporation, and polarization are performed to enhance performance of this compound. Additionally, advanced detection techniques are applied to showcase the capability of high quality BiI3 spectrometers. Overall, through this work, BiI3 is revealed as a potentially transformative material for nuclear security and radiation detection sciences. Dissertation Discovery Company and University of Florida are dedicated to making scholarly works more discoverable and accessible throughout the world. This dissertation, "Materials Development for Nuclear Security" by Paul M Johns, was obtained from University of Florida and is being sold with permission from the author. A digital copy of this work may also be found in the university's institutional repository, IR@UF. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation.