The high fracture toughness of stabilized zirconia makes it one of the most widely applicable high temperature structural materials. However, it is not typicality considered for optical applications since the microstructure achieved by traditional processing makes it opaque. The aim of this dissertation is to develop processing methods for the introducing new functionalities of light transparency and light emission (photoluminescence) and to understand the nanostructure-property relationships that make these functionalities possible. A processing study of rare-earth (RE) doped Zirconium Oxide (ZrO2, zirconia) via Current Activated Pressure Assisted Densification (CAPAD) is presented. The role of processing temperature and dopant concentration on the crystal structure, microstructure and properties of the RE: ZrO2 is studied. Microstructural shows sub-100 nm grain size and homogeneous dopant distribution. X-ray diffraction and Raman analysis show that with increased dopant concentration the material changes from monoclinic to tetragonal. Structural analysis shows the material shows high hardness and toughness values 30% greater than similarly processed yttria-stabilized zirconia. Despite birefringence in the tetragonal phase, optical characterization is presented showing the samples are both highly transparent and photo-luminescent. Special attention is paid to analyzing structural and photoluminescence development during densification, as well as the role of oxygen vacancies on the optical properties of the densified material. This material is shown to be a promising candidate for a number of applications including luminescence thermometry and high temperature light emission.

Experimental studies are presented that aim to utilize phase change materials (PCM's) to enhance thermal energy storage systems for concentrated solar thermal power (CSP) systems. Both laboratory scale and prototype flow loop scale experiments were conducted. Background and motivation of the system is presented followed by experimental results and experimental system design.

Laboratory experiments were performed to determine the effectiveness of various surface treatments on changing the nucleation kinetics and enhancing heat transfer in the system. Experimental data is presented to show the effectiveness of both surface finish and surface material treatments.

A large scale flow loop was designed and built to determine real heat transfer during solidification. Extensive design calculations were performed along with CAD design before the apparatus was constructed. Once the system was built, systematic testing and development led to a fully functional system ready for actual heat transfer testing.