Date of Award
Doctor of Philosophy
Materials Science and Engineering
Philip D. Rack
Charles L. Melcher, Claudia J. Rawn, Jason P. Hayward
The development and application of a combinatorial sputtering thin film technique to screen potential scintillation material systems was investigated. The technique was first benchmarked by exploring the binary lutetium oxide-silicon oxide material system, which successfully identified the luminescence phases of the system, Lu2SiO5 (LSO) and Lu2Si2O7 (LPS). The second application was to optimize the activator concentration in cerium doped LSO. The successfully optimized cerium concentration in the thin film LSO of 0.34 atomic percent was much greater than the standard cerium concentration in single crystal LSO. This lead to an intensive study based on temperature dependent steady-state and lifetime photoluminescence spectroscopy to understand the different concentration quenching mechanisms involved in the bulk single crystal versus the thin film LSO. The results were used to develop configuration coordinate models which were employed to explain the observed concentration dependent behavior. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer, and ultimately self-absorption. For the thin films it was found self-absorption was not a dominant factor due to the thin dimension of the film and also its nano-crystalline nature. Instead, the photoluminescence excitation and emission spectra as a function of concentration demonstrated the concentration quenching behavior was due to an increase in defect-mediated non-radiative transitions with increasing cerium. The final application of the thin film screening technique was the exploration of the ternary Lu2O3-SiO2-Al2O3 material system doped with cerium. It was found that the presence of aluminum and silicon hindered LSO and Al5Lu3O12 (LuAG) emission, respectively. However, the presence of aluminum was found to increase LPS emission intensity. The percent of aluminum in the LPS phase was estimated at 2.5 atomic percent.
Peak, Jonathan Daniel, "Thin Film Combinatorial Synthesis of Advanced Scintillation Materials. " PhD diss., University of Tennessee, 2010.