Date of Award
Doctor of Philosophy
Jacqueline A. Johnson
Justin S. Baba, Laurence F. Miller, Charles L. Melcher
Fluorochlorozirconate (FCZ) glass ceramics are versatile materials whose optical properties may be tuned through compositional or processing changes. For this work, FCZ glasses were synthesized, and then subsequently heat treated to create optically-active glass ceramics. The glasses and glass ceramics were characterized using a number of methods including differential scanning calorimetry, phosphorimetry, x-ray diffraction, and spectrophotometry. Samples were evaluated for applications in photovoltaics and computed radiography–especially those pertaining to intraoral dental radiography and portal imaging.
The ability of FCZ glass ceramics containing hexagonal barium chloride nanocrystals doped with the rare earth elements, holmium and europium, to downshift ultraviolet light to wavelengths more usable by polycrystalline silicon photovoltaic cells was investigated. The excitation spectra of FCZ glass ceramics doped or co-doped with divalent europium more closely match the solar spectrum at the earth’s surface than an undoped sample. The addition of holmium gives rise to additional emission nearer to the band gap energy of polycrystalline silicon photovoltaic cells. These materials may increase the efficiency of photovoltaic cells in solar energy applications.
The sodium fluoride content in FCZ glass-ceramic storage phosphor plates was varied to determine the effect on sample properties, including photostimulated luminescence (PSL) light output for computed radiography applications, including intraoral dental radiography. The percentage of sodium fluoride used in each sample composition had a marked effect on glass stability, transparency, thermal characteristics, and PSL performance. The PSL light output of the samples may be suitable for nondestructive testing, where dose is not a primary concern.
An FCZ glass ceramic was evaluated for use as a storage phosphor in gamma-ray imaging. Test images were made at 2 MeV energies using gap and step wedge phantoms. Gaps as small as 101.6 µm [micrometers] in a 440 stainless steel phantom were imaged using the sample imaging plate. Analysis of an image created using a depleted uranium step wedge phantom showed that PSL emission is proportional to incident energy at the sample and the estimated absorbed dose. The sample imaging plate has potential for nondestructive testing, as well as portal imaging applications, where it may provide geometric and dosimetric verification.
Leonard, Russell Lee, "Fluorochlorozirconate Glass Ceramics for Photovoltaic and Computed Radiography Applications. " PhD diss., University of Tennessee, 2015.