A 2 B 2 O 7 system compounds, which usually present three phase structures mainly based on the ionic radius ratios of r A and r B (r A /r B), have been studied for potential applications in many fields, such as thermal barrier coatings, luminescence powders, fast-ion conductors, photocatalysts, and matrices for immobilization of highly active radionuclides. Since 2005, La 2 Hf 2 O 7 was fabricated into transparent ceramics and much more attentions were paid on A 2 B 2 O 7 transparent ceramics for new applications. In this review, the development of A 2 B 2 O 7 system transparent ceramics was described. The structure characteristics, powder synthesis method, and sintering techniques of the final A 2 B 2 O 7 transparent ceramics were summarized. After that, the mostly reported A 2 Hf 2 O 7 , A 2 Zr 2 O 7 , and A 2 Ti 2 O 7 system transparent ceramics were systematically introduced. The potential application fields and future development trends were also discussed, focusing on scintillators, optical elements, and other luminescent materials.

Three-dimensional flowerlike europium-doped lanthanide molybdate [La2(MoO4)3:Eu] microarchitectures that exhibit efficient photoluminescence have been successfully synthesized via a facile hydrothermal process in the presence of the surfactant bis(2-ethylhexyl)sulfosuccinate (AOT). The La2(MoO4)3:Eu microspheres are well dispersed, have a uniform diameter of about 3 μm, and are composed of nanoflakes of about 30-nm thickness that connect to each other by both edge-to-edge and edge-to-flat-surface conjunctions with few surface-to-surface attachments. The surfactant NaAOT was found to play a crucial role in achieving the good dispersibility and uniform morphology of the final product, as compared to the same material but synthesized without the surfactant. The UV absorption results illustrate that there is a 20-nm blue shift of CT band relative to bulk materials, which can be attributed to the quantum size effects of the nanoflakes. These La2(MoO4)3:Eu microspheres show efficient photoluminescence that is associated with the well-crystallized structures of the microarchitectures.

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