title: Comparative investigations of the crystal structure and photoluminescence property of eulytite-type Ba3Eu(PO4)3 and Sr3Eu(PO4)3.
abstract: In this study, the Ba3Eu(PO4)3 and Sr3Eu(PO4)3 compounds were synthesized and the crystal structures were determined for the first time by Rietveld refinement using powder X-ray diffraction (XRD) patterns. Ba3Eu(PO4)3 crystallizes in cubic space group I43d, with cell parameters of a = 10.47996(9) Å, V = 1151.01(3) Å(3) and Z = 4; Ba(2+) and Eu(3+) occupy the same site with partial occupancies of 3/4 and 1/4, respectively. Besides, in this structure, there exists two distorted kinds of the PO4 polyhedra orientation. Sr3Eu(PO4)3 is isostructural to Ba3Eu(PO4)3 and has much smaller cell parameters of a = 10.1203(2) Å, V = 1036.52(5) Å(3). The bandgaps of Ba3Eu(PO4)3 and Sr3Eu(PO4)3 are determined to be 4.091 eV and 3.987 eV, respectively, based on the UV-Vis diffuse reflectance spectra. The photoluminescence measurements reveal that, upon 396 nm n-UV light excitation, Ba3Eu(PO4)3 and Sr3Eu(PO4)3 exhibit orange-red emission with two main peaks at 596 nm and prevailing 613 nm, corresponding to the (5)D0 → (7)F1 and (5)D0 → (7)F2 transitions of Eu(3+), respectively. The dynamic disordering in the crystal structures contributes to the broadening of the luminescence spectra. The electronic structure of the phosphates was calculated by the first-principles method. The analysis elucidats that the band structures are mainly governed by the orbits of phosphorus, oxygen and europium, and the sharp peaks of the europium f-orbit occur at the top of the valence bands.
authors: School of Materials Science and Technology, National Laboratory of Mineral Materials, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, China University of Geosciences (Beijing), Beijing, 100083, China. huang118@cugb.edu.cn.
authors: Haipeng
authors: H
authors: Ji
authors: Zhaohui
authors: Z
authors: Huang
authors: Zhiguo
authors: Z
authors: Xia
authors: Maxim S
authors: MS
authors: Molokeev
authors: Xingxing
authors: X
authors: Jiang
authors: Zheshuai
authors: Z
authors: Lin
authors: Victor V
authors: VV
authors: Atuchin