Extrinsic defect structure of RE3Al5O12 garnets

RE3Al5O12 garnets (where RE represents rare earth atoms Lu-Gd and Y) are technologically important, particularly for optical applications. However, the performance of these materials suffers from the existence of point defects, which are responsible for both delayed and reduced light output in Ce:Y3Al5O12 (Ce:Yag) scintillators. The complex garnet crystal prevents a straightforward description of the defects responsible for decreased performance. In this paper, we employ atomistic simulation techniques to reveal non-intuitive features of the extrinsic defect structure. Specifically: Me2+ dopants (ranging in ionic size from Mg2+-Ba2+) are predicted to reside on RE sites with oxygen vacancies as charge compensating defects and Me4+ dopants (from Ti4+-Pb4+) reside on both RE and Al sites and are predicted to be charge compensated by RE vacancies. These results predict the defects resulting from common Me2+ impurities, as well as explain why Me4+ doping is not effective in improving RE3Al5O12 scintillator performance. The predicted extrinsic defects in RE3Al5O12 associated with Me2+ (bottom left) and Me4+ (upper right) doping. Small and large grey atoms represent Al and RE lattice atoms respectively. Oxygen atoms are not shown.