Dissertation
IMPROVED CZOCHRALSKI GROWTH AND ACTIVATOR EFFICIENCY OF CERIUM DOPED YTTRIUM ALUMINUM GARNET BY DEFECT ENGINEERING
Doctor of Philosophy (PhD), Washington State University
01/2013
Handle:
https://hdl.handle.net/2376/4765
Abstract
The past several decades have seen a genuine surge in development of scintillator materials for use in a multitude of applications ranging from high energy physics to medical imaging. Despite the rapid materials discovery that has been undertaken in the search for better scintillators, a host of defects still limit scintillator performance in many promising materials. Thus the key to tapping into a scintillators full potential lies in understanding and modifying their defect structure through a process known as defect engineering.
One such promising visible light scintillator is cerium doped yttrium aluminum garnet (Ce:YAG). Despite characteristics that make Ce:YAG an excellent yellow phosphor that see it commonly used in fluorescent lights and while light LEDs, performance hindering defects severely limited its potential as a bulk scintillator, a critical defect being that of UV defect luminescence. By successfully building a new Czochralski (CZ) furnace, samples could be grown with careful control over growth conditions to study and reduce these defects. All samples were grown in similar conditions by the CZ method with a (111) oriented undoped YAG seed.
Several original approaches were developed in this study to reduce defects or mitigate their influence. The first method of solving the problem relied on recognizing that what many in the past identified as visible scintillation light was in fact UV defect luminescence. By using multiple photodetectors it was demonstrated that when higher cerium doping levels are involved in Ce:YAG, luminescence is not decreased due to self-absorption as previously thought, but rather UV defect emission is quenched in favor of visible emission.
Once established, new avenues of research became available. Another study demonstrates Ce:YAG grown by the Czochralski method in alumina rich conditions is an effective method for reducing the number of UV producing yttrium antisite defects. This culminated in record energy resolution of Ce:YAG in a bulk sample.
A final study investigated Ce:YAG grown in a rhenium crucible, both to investigate the future of high temperature oxide crystal growth, and to investigate potential benefits of Ce:YAG growth outside of an iridium crucible. The study showed significant promise in both of these categories.
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Details
- Title
- IMPROVED CZOCHRALSKI GROWTH AND ACTIVATOR EFFICIENCY OF CERIUM DOPED YTTRIUM ALUMINUM GARNET BY DEFECT ENGINEERING
- Creators
- Drew Thomas Haven
- Contributors
- Kelvin G Lynn (Advisor)Matthew D McCluskey (Committee Member)Gary S Collins (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Materials Science and Engineering Program
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 158
- Identifiers
- 99900581744001842
- Language
- English
- Resource Type
- Dissertation