Aluminum and Gallium Substitution in Yttrium and Lutetium Aluminum–Gallium Garnets: Investigation by Single-Crystal NMR and TSL Methods

Abstract

The work reports the results on 71 Ga and 27 Al NMR investigation of the gallium and aluminum ions distribution over tetrahedral and octahedral positions in the Y 3 Al 5– x Ga x O 12:Ce single crystals and Lu 3 Al 5– x Ga x O 12:Ce single-crystalline epitaxial films. The gallium content x varies between 0 and 5 in crystals and between 0.3 and 2 in films.. We find that in both the Y- and Lu-based solid solutions the larger gallium ions are preferably located at the tetrahedral position while the smaller aluminum ions prefer the octahedral position of the garnet host. Based on NMR data, the dependence of fractional occupation parameters of the tetrahedral site of Ga and Al ions on the Ga content is determined. In particular, in the Y 3 Al 2 Ga 3 O 12:Ce crystal only 28% of Ga ions occupy octahedral sites, whereas 72% occupy tetrahedral ones. NMR investigations suggest that observed nonmonotonic dependences of electron trap depths monitored by thermally stimulated luminescence of Y 3 Al 5– x Ga x O 12:Ce complex garnets on the Ga content are related to preferential localization of the Ga and Al ions over the tetrahedral and octahedral positions of the garnet lattice, respectively. Our data confirm that the tetrahedral site preference (over the octahedral site) for the Ga occupation is an intrinsic property of the mixed Y 3 (Lu 3 )Al 5– x Ga x O 12 garnets.