Extrinsic defect structure of RE₃Al₅O₁₂ garnets

Abstract

Abstract RE 3 Al 5 O 12 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:Y 3 Al 5 O 12 (Ce:YAG) scintillators. The complex garnet crystal structure prevents a straightforward description of the defects responsible for decreased performance. In this paper, we employ atomistic simulation techniques to reveal nonintuitive features of the extrinsic defect structure. Specifically: Me 2+ dopants (ranging in ionic size from Mg 2+ –Ba 2+ ) are predicted to reside on RE sites with oxygen vacancies as charge compensating defects and Me 4+ dopants (from Ti 4+ –Pb 4+ ) 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 Me 2+ impurities, as well as explain why Me 4+ doping is not effective in improving RE 3 Al 5 O 12 scintillator performance. magnified image The predicted extrinsic defects in RE 3 Al 5 O 12 associated with Me 2+ (bottom left) and Me 4+ (upper right) doping. Small and large grey atoms represent Al and RE lattice atoms respectively. Oxygen atoms are not shown. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)