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.

Trends in Search for Bright Mixed Scintillators

“…By the analogy with LGSO:Ce, in the garnet structure of YAGG:Ce the tetrahedral and octahedral sites are enriched with Ga 3+ and Al 3+ , correspondingly. This was proved by the NMR analysis based on determination of 27 Al, 71 Ga, and 69 Ga isotope concentrations . Ga 3+ ions preferably occupy the tetrahedral sites, while Al 3+ ions preferably occupy the octahedral sites.…”

Modeling and Assessment of Afterglow Decay Curves from Thermally Stimulated Luminescence of Complex Garnets

“…The latter can appear due to the fluctuations of the the bottom of the conduction band appearing in mixed solid solutions 41,42 and distortion of the vacuum levels of the defects due to statistical variation of the cations distribution in the second coordination sphere around the defect. 19,43 In the Fig. 6 fluctuations of the bottom of the conduction band and energy level of the defects are schematically shown by two bell shaped curves.…”

Engineering of bulk and fiber-shaped YAGG:Ce scintillator crystals

“…The decay time sharply drops between the samples with 40 and 60% Ga, though the common trend of decay time decrease with Ga concentration is clear. Recently 21 , it was shown that Ga 3+ Please do not adjust margins Please do not adjust margins preferably occupies the tetrahedral sites in YAGG (though larger Ga 3+ atoms was supposed to occupy first the larger octahedral sites). The interval between 40 and 60 % of Ga corresponds to the situation when the number of Ga atoms exceeds the number of Al atoms and Al 3+ /Ga 3+ substitution into octahedral sites starts.…”