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Weiwei Zuoa) and Meifang Zhu State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, Shanghai, Shanghai 201260, China

Dianguang Liu,b) Yigao Chen, Meng Zhu, Haoran Hong, Chengyu Yang, and Yiguang Wangc) State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, Shanxi 710072, China

Jinling Liu State Key Laboratory of Traction Power, School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China

Linan An Department of Materials Science and Engineering, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida 32816, USA (Received 30 September 2015; accepted 23 November 2015)

ZrO2:Eu31 hollow spheres were successfully fabricated with the resin microspheres as the template. The sample characterizations were carried out by means of x-ray diffraction (XRD), scanning electron microscope (SEM), and photoluminescence spectra. XRD results revealed that Eu31-doped samples were pure t-ZrO2 phase after being calcined at 873 K. SEM results exhibited that this Eu31 doped ZrO2 was hollow spheres; the diameter and thickness of which were about 450 and 50 nm, respectively. Upon excitation at 394 nm, the orange-red emission bands at the wave length longer than 570 nm were from 5D0 ! 7FJ (J 5 1, 2) transitions. The asymmetry ratio of (5D0 ! 7F2)/(5D0 ! 7F1) intensity is about 1.61, 1.26, 1.42, 1.42, 1.40, and 1.38 for the Eu31 concentration 0.4, 0.7, 1.0, 1.5, 2.0, and 2.5 mol%, respectively. These values suggest that the asymmetry ratio of Eu31 ions is independent of the doping concentration. The optimal doping concentration of Eu31 ions in ZrO2 is 1.5 mol%. According to Dexter’s theory, the critical distance between Eu31 ions for energy transfer was determined to be 16 Å.

Contributing Editor: Xiaobo Chen Address all correspondence to these authors. a) e-mail: [email protected] b) Co-first author c) e-mail: [email protected] DOI: 10.1557/jmr.2015.375

Fe2O3 flower-like microspheres,13 urchin-like WO3 and MnWO4 microstructures,14,15 cactus-like b-Ga2O3 microarchitectures,16 dandelion-like ZnO and CuO architectures,17,18 3D hierarchical MWO4 (M 5 Mn, Bi, Ba, and Pb), and MMoO4 (M 5 Fe, Pb, and Ba) superstructures,9,19–23 which have been fabricated from low dimensional nanobuilding units by bottom-up approaches. Since sphere morphology of phosphor is favorable for high brightness and high resolution, spherical structured particles have been interestingly studied in these years.16–18 The selection of host materials for RE ions is crucial to obtain large luminescence signals.14 Materials with low phonon energies present small nonradiative losses owing to the multiphonon relaxation, and consequently, the luminescence efficiency is enhanced. A suitable host must also present large optical band gap along with good solubility and stability. Zirconia is a suitable host for RE material because it offers a large transparency window from the short ultraviolet to the near infrared