Date of Award
Doctor of Philosophy
Jacqueline A. Johnson
Russel L. Leonard, Claudia J. Rawn, Feng-Yuan Zhang
Optically active materials are used in many biomedical applications ranging from medical imaging to light therapies. Investigating the effects of differing nanostructure configurations on the optical performance of these materials can improve tunability, efficiency, and practicality for their respective applications. This work utilizes pulsed laser deposition (PLD) to develop nanostructured thin films and determines their optical performance for applications in computed radiography for medical imaging and in LEDs which can be used in biomedical applications such as photobiomodulation.
In computed radiography, scattering of the stimulation light by the storage phosphor crystal grain boundaries in imaging plates negatively impacts spatial resolution. Storage phosphor plates with thinner phosphor layers have been developed to reduce scattering distance and increase spatial resolution, although at the expense of reduced x-ray absorption. A transparent or translucent nanostructured film, containing a much higher percentage of storage phosphor crystals achievable in bulk glass-ceramic materials made by conventional methods, may have acceptable photostimulated luminescence efficiency and imaging performance characteristics greater than commercial imaging plates. In an attempt to achieve a nanostructured film with superior performance in x-ray imaging, a glass-ceramic imaging plate for computed radiography was synthesized via PLD for the first time. The imaging plate was comprised of Eu-doped BaCl2 crystallites and an amorphous matrix.
Nanolayered films comprising of BaF2, Eu2O3, and Al2O3 were synthesized via PLD with differing layered configurations to manipulate the coordinate surrounds of the europium dopant and determine its effects on optical properties. TEM cross-section analysis was conducted to verify the desired nano-layering. Different post-deposition heat treatments were investigated, and the films were evaluated for applications as a phosphor layer for UV-pumped white light LEDs which can be used for solid-state lighting and biomedical light therapies. A Mn dopant was added to europium to discover the threshold for the amount of manganese necessary to optically influence the nanolayered films. Although Mn/Eu co-doping did not prove advantageous for white light LEDs, all nanostructures of Eu-doped films have the potential for the desired application.
Nanoscale control of optically-active thin films was demonstrated using pulsed laser deposition. Determining the effects of differing nanostructures on optical properties can lead to improvements in certain biomedical applications.
Bond, Charles William, "Optically Active Rare-Earth Doped Films Synthesized by Pulsed Laser Deposition for Biomedical Applications. " PhD diss., University of Tennessee, 2021.