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Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd 3 Al 5 O 12 )

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ABSTRACT

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd3Al5O12, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd3+ to the activator. Ce3+ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out.

No MeSH data available.


Appearance of the Gd3(Al2Ga3)O12 single crystals doped with 1 at% of Ce3+ (a) and 1 at% of Pr3+ (b). Part (a) reproduced with permission from [24] and part (b) reproduced with permission from [25], copyright 2012 by Elsevier.
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Figure 2: Appearance of the Gd3(Al2Ga3)O12 single crystals doped with 1 at% of Ce3+ (a) and 1 at% of Pr3+ (b). Part (a) reproduced with permission from [24] and part (b) reproduced with permission from [25], copyright 2012 by Elsevier.

Mentions: There are two primary ways to stabilize the garnet lattice of GAG, as can be perceived from the crystal structure shown in figure 1, with the first one partially replacing the Al sites with suitably larger trivalent ions to enlarge the dodecahedral interstices via forming Gd3(Al1−xMx)5O12 solid solution and the second one being partially replacing Gd3+ with a smaller Ln3+ to form (Gd1−xLnx)3Al5O12. Ga3+ is the main choice in the former case, and Gd3Ga5O12 (GGG), known as a thermodynamically stable garnet host for phosphors and solid lasers [2], is an extreme example. The effectiveness of Ga3+ doping was experimentally demonstrated by Chiang et al [23], who found that phase-pure garnet can be crystallized from chemically precipitated precursors at ∼1400 °C in the presence of 10 at% of Ga3+ and the crystallization temperature decreases to 1300 °C with 20 at% of Ga3+ addition. Without Ga3+ doping, only a phase mixture of LnAP, LnAG and amorphous alumina was formed. By applying the same stabilization strategy, Kamada et al were able to grow two-inch-diameter Gd3(Al2Ga3)O12:Ce3+ single crystals by the Czochralski (Cz) method using [100] oriented seeds [24] and Gd3(Ga,Al)5O12:Pr3+ single crystals by a micro-pulling down (μ-PD) technique [25] (figure 2). Though Ga3+ was thought to exclusively replace Al3+ in these studies, atomistic modeling using the static lattice computational approach and pairwise (Buckingham) interatomic potentials by Maglia et al [26] revealed that Ga3+, though it prefers to take the octahedral Al3+ site, can also be inserted into the dodecahedral position of Gd3+ with the generation of anti-site defects owing to its relatively large ionic radius. In addition, suppressing activator oxidation (such as Pr3+, Ce3+, and Tb3+) and Ga3+ reduction should be made at the same time to avoid lattice defects and deterioration of optical performance.


Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd 3 Al 5 O 12 )
Appearance of the Gd3(Al2Ga3)O12 single crystals doped with 1 at% of Ce3+ (a) and 1 at% of Pr3+ (b). Part (a) reproduced with permission from [24] and part (b) reproduced with permission from [25], copyright 2012 by Elsevier.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036492&req=5

Figure 2: Appearance of the Gd3(Al2Ga3)O12 single crystals doped with 1 at% of Ce3+ (a) and 1 at% of Pr3+ (b). Part (a) reproduced with permission from [24] and part (b) reproduced with permission from [25], copyright 2012 by Elsevier.
Mentions: There are two primary ways to stabilize the garnet lattice of GAG, as can be perceived from the crystal structure shown in figure 1, with the first one partially replacing the Al sites with suitably larger trivalent ions to enlarge the dodecahedral interstices via forming Gd3(Al1−xMx)5O12 solid solution and the second one being partially replacing Gd3+ with a smaller Ln3+ to form (Gd1−xLnx)3Al5O12. Ga3+ is the main choice in the former case, and Gd3Ga5O12 (GGG), known as a thermodynamically stable garnet host for phosphors and solid lasers [2], is an extreme example. The effectiveness of Ga3+ doping was experimentally demonstrated by Chiang et al [23], who found that phase-pure garnet can be crystallized from chemically precipitated precursors at ∼1400 °C in the presence of 10 at% of Ga3+ and the crystallization temperature decreases to 1300 °C with 20 at% of Ga3+ addition. Without Ga3+ doping, only a phase mixture of LnAP, LnAG and amorphous alumina was formed. By applying the same stabilization strategy, Kamada et al were able to grow two-inch-diameter Gd3(Al2Ga3)O12:Ce3+ single crystals by the Czochralski (Cz) method using [100] oriented seeds [24] and Gd3(Ga,Al)5O12:Pr3+ single crystals by a micro-pulling down (μ-PD) technique [25] (figure 2). Though Ga3+ was thought to exclusively replace Al3+ in these studies, atomistic modeling using the static lattice computational approach and pairwise (Buckingham) interatomic potentials by Maglia et al [26] revealed that Ga3+, though it prefers to take the octahedral Al3+ site, can also be inserted into the dodecahedral position of Gd3+ with the generation of anti-site defects owing to its relatively large ionic radius. In addition, suppressing activator oxidation (such as Pr3+, Ce3+, and Tb3+) and Ga3+ reduction should be made at the same time to avoid lattice defects and deterioration of optical performance.

View Article: PubMed Central - PubMed

ABSTRACT

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd3Al5O12, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd3+ to the activator. Ce3+ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out.

No MeSH data available.