Characterizing and Modifying Defects that Trap Excitons in Yttrium Aluminum Garnets Doped with Rare-Earth Elements

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Technical: This project aims for greater understanding of the interactions between excitons and crystalline defects in rare earth doped yttrium aluminum garnet (YAG) scintillator crystals. The approach toward more in-depth understanding and control of exciton dynamics is through their interactions with activating impurities and lattice defects. Lattice defects in the YAG structure will be characterized using positron lifetime spectrometry through a comprehensive study of their types, sizes and concentrations. Positron parameters will be correlated with optical measurements of exciton behavior, photon emission, and scintillation properties. The correlation between positron parameters and optical properties will be monitored as a function of growth conditions, choice of rare-earth dopant, doping levels, deviations from stoichiometry and postgrowth treatments. The correlation will further be examined following processing steps that include thermal annealing under different atmospheres. Results of the characterizations will be used to modify synthesis and growth conditions in order to improve optical properties. Non-technical: The project addresses basic research issues in a topical area of materials science with technological relevance in electronics and photonics. Through greater understanding of the interactions of excitons with defects this research is expected to lead to significant improvements in scintillator performance. Scintillator materials convert various types of radiation into photons, which can then be collected and analyzed. Two important application areas are medical diagnostics, and gamma and neutron radiation detection. The relationship between crystalline defects and scintillator performance is an important topic and at the present time not well understood. The results of these studies will help to understand how to improve scintillator efficiency by leading to the design of improved scintillator compositions and structure. The research will enhance understanding of defect formation in ionic crystals and selection of improved methods of synthesis/processing for superior optical properties. The project will integrate research and education of undergraduate and graduate student participants. Training will be in a multi-disciplinary environment of basic and applied physics, materials science, electronics and photonics. In addition to providing support and mentoring of graduate students, the PIs will motivate undergraduate and high school students through a web site and make presentations to students on and off campus. The PIs will create a diverse research group that includes women and minority group members. Research results will be disseminated through publications in premier journals and via presentations at conferences and in seminars.