Crystal Structure Stabilization of Gadolinium Aluminum Garnet (Gd₃Al₅O₁₂) and Photoluminescence Properties

Abstract

To suppress the thermal decomposition and to stabilize the crystal structure of Gd3Al5O12 (GdAG) garnet, doping GdAG with smaller Ln3+ (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, respectively) to form (Gd,Ln)AG solid solutions was proposed in work. Carbonate precursors of (Gd,Ln)AG with an approximate composition of (NH4)x(Gd,Ln)3Al5(OH)y(CO3)z•nH2O were synthesized via coprecipitation from a mixed solution of ammonium aluminum sulfate and rare earth nitrate, using ammonium hydrogen carbonate as the precipitant. The precursors and the calcination derived oxides were characterized using FT-IR spectroscopy, DTA/TG, XRD, BET and FE-SEM. The results showed that smaller Ln3+ doping can indeed stabilize GdAG against its thermal decomposition to a mixture of GdAlO3 (GdAP) and Al2O3 phases at elevated temperatures and at the same time effectively lowers the temperature for garnet crystallization. The carbonate precursors are loosely agglomerated and the resultant (Gd,Ln)AG powders show good dispersion and a fairly uniform particle morphology. The (Gd,Ln)AG solid solutions exhibit decreasing lattice parameters along with decreasing radius of the dopant ions at the same dopant content of 50 at%. Photoluminescence properties of some of the garnet solid solutions are also studied. The materials developed herein may potentially be used for photoluminescent and scintillation applications.

Luminescence Behavior of Tm³⁺ Activated GdAlO₃ Phosphors Synthesized Using Solid-Reaction Method

“…2(b). These could be GAP phase formed or transformed α-alumina phase [18]. Besides, agglomerates of un-reacted nano-sized particles are still observable, in agreement with the XRD data.…”

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

“…This indicates that stable garnet solid solutions exist if the average ionic size of (Ln 1 ,Ln 2 ) 3+ pair lies in between those of Gd 3+ (0.1053 nm for CN = 8) and Tb 3+ , in agreement with the fact that TbAG [28–30] and even (Gd 0.9 Lu 0.1 )AG [31, 32] can be further doped with larger Eu 3+ (0.1066 nm, CN = 8) and Ce 3+ (0.1143 nm, CN = 8) for luminescence. Taking the average ionic size of (Gd 0.9 Lu 0.1 ) 3+ (~0.1045 nm) as a standard, Li et al [33] analyzed the minimum amounts of various small Ln 3+ that are needed for GAG stabilization, and the x value was predicted to be ∼0.5 for Tb 3+ , 0.3 for Dy 3+ (0.1027 nm), 0.22 for Y 3+ (0.1019 nm), 0.2 for Ho 3+ (0.1015 nm), 0.15 for Er 3+ (0.1004 nm), 0.13 for Tm 3+ (0.0994 nm), and 0.11 for Yb 3+ (0.0985 nm). Practical powder synthesis indeed shows that (Gd 1− x Ln x )AG garnet can be obtained in high phase purity with incorporation of the calculated amount of dopant in each case (figure 5).…”

Cerium-doped gadolinium-scandium-aluminum garnet powders: synthesis and use in X-ray luminescent diamond composites

“…Moreover, in this case, the substitution begins from the tetrahedral garnet site: Gd3Al2Al3O12 =>Gd3Al2Ga3O12 =>Gd3Ga2Ga3O12. The alternative method involves a decrease in the ionic radius of the dodecahedral site by partial replacement of gadolinium (r VIII (Gd 3+ ) = 1.053Å [16]) by ions with a smaller ionic radii, e.g., lutetium (r VIII (Lu 3+ ) = 0.977Å [16]), while keeping the octahedral and tetrahedral sites unchanged [14,[17][18][19]. At the same time, scandium can replace both dodecahedral and octahedral sites of the garnet lattice in significant amounts [20], which makes it possible to implement both approaches simultaneously and decrease the size of the dodecahedral site.…”