Phase stabilization in transparent Lu2O3:Eu ceramics by lattice expansion

• Published in: Optical materials 2012-11, Vol.35 (1), p.74-78
• Main Authors: Seeley, Z.M., Dai, Z.R., Kuntz, J.D., Cherepy, N.J., Payne, S.A.
• Format: Article
• Language: English
• Subjects: Densification; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Gadolinium oxide; Lutetium oxide; Optical materials; Optics; Physics; Sinter-HIP; Transparent ceramic
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2012.07.005

► Europium segregates from Lu2O3:Eu during processing of transparent ceramics. ► High concentrations of Eu at grain triple points precipitates into a secondary phase. ► Addition of gadolinium stretches the cubic lattice parameter allowing Eu to stay in solid solution. ► Highly transparent Gd0.6Lu1.3Eu0.1O3 ceramic was fabricated without secondary phase. Gadolinium lutetium oxide transparent ceramics doped with europium (Gd,Lu)2O3:Eu were fabricated via vacuum sintering and hot isostatic pressing (HIP). Nano-scale starting powder with the composition GdxLu1.9−xEu0.1O3 (x=0, 0.3, 0.6, 0.9, 1.0, and 1.1) were uniaxially pressed and sintered under high vacuum at 1625°C to obtain ∼97% dense structures with closed porosity. Sintered compacts were then subjected to 200MPa argon gas at temperatures between 1750 and 1900°C to reach full density. It was observed that a small portion of the Eu3+ ions were exsolved from the Lu2O3 cubic crystal lattice and concentrated at the grain boundaries, where they precipitated into a secondary monoclinic phase creating optical scattering defects. Addition of Gd3+ ions into the Lu2O3 cubic lattice formed the solid solution (Gd,Lu)2O3:Eu and stretched the lattice parameter allowing the larger Eu3+ ions to stay in solid solution, reducing the secondary phase and improving the transparency of the ceramics. Excess gadolinium, however, resulted in a complete phase transformation to monoclinic at pressures and temperatures sufficient for densification. Light yield performance was measured and all samples show equal amounts of the characteristic Eu3+ luminescence, indicating gadolinium addition had no adverse effect. This material has potential to improve the performance of high energy radiography devices.