title: Crystal structure evolution and luminescence properties of color tunable solid solution phosphors Ca(2+x)La(8-x)(SiO4)(6-x)(PO4)xO2:Eu(2+).
abstract: A series of apatite solid solution phosphors Ca(2+x)La(8-x)(SiO4)(6-x)(PO4)xO2:Eu(2+) (x = 0,2,4,6) were synthesized by a conventional high-temperature solid-state reaction. The phase purity was examined using XRD, XPS and XRF. The crystal structure information, such as the concentration, cell parameters and occupation rate, was analyzed using a Rietveld refinement, demonstrating that the Eu(2+) activated the Ca2La8(SiO4)6O2 and Ca8La2(PO4)6O2 to form continuous solid solution phosphors. Different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. Two kinds of Eu(2+) ion sites were proved using low temperature PL spectra (8k) and room temperature decay curves. The substitution of large La(3+) ions by small Ca(2+) ions induced a decreased crystal field splitting of the Eu(2+) ions, which caused an increase in emission energy from the 5d excited state to the 4f ground state and a resultant blue-shift from 508 nm to 460 nm. Therefore, with the crystal structure evolution, the emitted color of the series of phosphors could be tuned from green to blue by adjusting the ratio of Ca/La.
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Yufei
authors.initials: Y
authors.lastname: Xia
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Yan-gai
authors.initials: YG
authors.lastname: Liu
authors.affiliation: Laboratory of Crystal Physics, Kirensky Institute of Physics, SB RAS, Krasnoyarsk 660036, Russia and Department of Physics, Far Eastern State Transport University, Khabarovsk 680021, Russia.
authors.forename: Maxim S
authors.initials: MS
authors.lastname: Molokeev
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Ming
authors.initials: M
authors.lastname: Guan
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Huang
authors.affiliation: School of Materials Science and Technology, Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing, 100083, China. liuyang@cugb.edu.cn.
authors.forename: Minghao
authors.initials: M
authors.lastname: Fang