Full Length Article Structures and luminescent properties of single-phase La 5.90 À x Ba 4 þ x (SiO 4 ) 6 À x (PO 4 ) x F 2 :0.10Ce 3 þ phosphors Qingfeng Guo, Libing Liao n , Lefu Mei n , Haikun Liu Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials. School of Materials Sciences and Technology, China University of Geosciences, Beijing 100083, China article info Article history: Received 22 July 2015 Accepted 10 December 2015 Available online 19 December 2015 Keywords: Apatite Structure Phosphor Photoluminescence abstract A series of blue-emitting La 5.90 Àx Ba 4 þx (SiO 4 ) 6Àx (PO 4 ) x F 2 :0.10Ce 3 þ (x ¼ 0, 1, 2, and 3) phosphors with apatite structure were synthesized by a solid-state reaction. The crystal structure and the photo- luminescence properties were investigated in detail. The crystallographic occupancy of Ce 3 þ in La 2.90 Ce 0.10 Ba 7 (SiO 4 ) 3 (PO 4 ) 3 F 2 and La 5.90 Ce 0.10 Ba 4 (SiO 4 ) 6 F 2 were studied based on Rietveld refinements results and the crystal chemistry rules. La 5.90Àx Ba 4 þx (SiO 4 ) 6 Àx (PO 4 ) x F 2 :0.10Ce 3 þ exhibited strong blue light emission in the range of 407–414 nm with high thermal stability upon excitation at 276 nm. Besides, the activation energy E of La 5.90 Ce 0.10 Ba 4 (SiO 4 ) 6 F 2 and La 2.90 Ce 0.10 Ba 7 (SiO 4 ) 3 (PO 4 ) 3 F 2 phosphors were calculated to be 0.152 and 0.177eV. These results suggest that La 5.90Àx Ba 4 þx (SiO 4 ) 6Àx (PO 4 ) x F 2 :0.10Ce 3 þ is a potential blue phosphor candidate for near-UV-pumped w-LEDs. & 2015 Elsevier B.V. All rights reserved. 1. Introduction In recent years, researchers have paid much attention to the luminescent materials for white light-emitting diodes (w-LEDs) because of the higher energy-efficiency, longer life, higher relia- bility and safety [1,2]. In general, the conventional way to fabricate white LEDs is based on a combination of yellow Y 3 Al 5 O 12 :Ce 3 þ (YAG:Ce) phosphor and blue LED [3]. Unfortunately, it exhibits a high correlated color temperature and a poor color rendering index because that YAG:Ce 3 þ phosphor lacks red emitting con- tribution [4]. Making a coating of three color (blue, green, and red) emitting phosphors on the top of NUV chip to obtain w-LEDs has attracted a large amount of interest. The rare earth ions play an important role in display and lighting fields for their 5d-4f or 4f-4f transitions [5,6], among which Ce 3 þ is a kind of important activator ions for novel phosphors with a wide range of emission due to the transition between the 4f 1 ground state and the crystal field components of the 5d excited state configuration [7,8]. Compounds with apatite structure have been widely used as host lattices in recent years, such as Sr 10 (PO 4 ) 6 O:Eu 2 þ [9], and Ca 8 Gd 2 (PO 4 ) 6 O 2 :Eu 2 þ ,Eu 3 þ [10], Ca 10 (SiO 4 ) 3 (SO 4 ) 3 F 2 :Eu 2 þ [11], Ca 2 Gd 8 (SiO 4 ) 6 O 2 :Eu 3 þ [12]. Fluoride-containing apatite structure compounds doped with rare-earth ions have great potential application due to their adjustable luminescence properties caused by the introduce of fluoride ions in the host lattice, which has been widely investigated, such as Ca 9 Mg(PO 4 ) 6 F 2 :Eu 2 þ , Mn 2 þ [13], Ba 10 F 2 (PO 4 ) 6 :Dy 3 þ [14], La 6 Ba 4 (SiO 4 ) 6 F 2 :Ce 3 þ , Tb 3 þ [15]. Based on the adjustable crystal field environment and interesting crystal chemistry, apatite-related structures acting as phosphor hosts have attracted growing interest [16,17]. In this paper, the photoluminescence property and structure of La 5.90 Àx Ba 4 þx (SiO 4 ) 6 Àx (PO 4 ) x F 2 :0.10Ce 3 þ was investigated in detail over the range x ¼ 0–3. 2. Experimental 2.1. Synthesis procedures A series of La 5.90 Àx Ba 4 þ x (SiO 4 ) 6 Àx (PO 4 ) x F 2 :0.10Ce 3 þ (x ¼ 0, 1, 2, and 3) phosphors were prepared by a traditional high temperature solid-state reaction. BaCO 3 (Aldrich, 99.9%), SiO 2 (Aldrich, 99.9%), NH 4 H 2 PO 4 (Aldrich, 99.9%), La 2 O 3 (Aldrich, 99.995%), and CeO 2 (Aldrich, 99.995%) were used as starting materials. The starting materials were mixed and ground according to the given stoi- chiometric ratio firstly. Then, the mixture was pre-heated at 750 °C for 3 h in air atmosphere in alumina crucibles. After cooling to room temperature, the preliminary products were placed into an alumina crucible and were heated at 1400 °C for 4 h in a reducing atmosphere with flowing gas (10% H 2 þ 90% N 2 ) with the flow rate of 0.5 L/min. Then the products were cooled to room temperature naturally. Finally, the products were ground again into powder for further analysis. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.12.013 0022-2313/& 2015 Elsevier B.V. All rights reserved. n Corresponding authors. Tel./fax: þ86 10 8233 1701. E-mail addresses: clayl@cugb.edu.cn (L. Liao), mlf@cugb.edu.cn (L. Mei). Journal of Luminescence 172 (2016) 191–196