Synthesis and site-selective photoluminescence property of Ca 8 La 2 (PO 4 ) 6 O 2 : Ce 3+
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Synthesis and site-selective photoluminescence property of Ca8La2(PO4)6O2: Ce3+ Ge Zhu1, Yurong Shi1, Masayoshi Mikami2,Yasuo Shimomura2, and Yuhua Wang1* 1
Department of Materials Science, School of PhysicalScience and Technology, Lanzhou University, Lanzhou, 730000, China 2
Mitsubishi Chemical Group Science and Technology Research Center, Yokohama 227-8502, Japan ABSTRACT A series of Ce3+ doped Ca8La2(PO4)6O2 phosphors with tunable emission were successfully synthesized by traditional solid state reaction. The crystal structure and photoluminescence properties were studied through X-ray diffraction, photoluminescence excitation and emission spectra. The results indicated that Ca8La2(PO4)6O2:Ce3+ exhibited color-tunable emission due to the 5d-4f transitions of Ce3+ ions under different wavelength excitation. The optimal doping content of Ce3+ ions in Ca8La2(PO4)6O2 was found to be 5 mol%. The site-selective photoluminescence property and the reason for red-shift of the emission band along with Ce3+ content and the excitation wavelength were also studied in detail. INTRODUCTION It is well known that apatite is an important family of materials with wide applications in catalysis, environmental remediation and ceramic membranes. Apatite contains a large number of inorganic compounds with the general formula M10(EO4)6X2, where M is a univalent to trivalent cation (Ca2+, Sr2+, Ba2+, Cd2+, Eu3+, Y3+, La3+, Na+, K+, etc.), E is a tetravalent to hexavalent element (P5+, V5+, As5+, Si4+, Ge4+, S6+, Cr6+, etc.), and X represents anions OH-, F-, Cl-, Br-, I-, and O2- [1,2]. Apatite crystallizes in the hexagonal system with space group P63/m, which is characterized by the presence of two cationic sites labeled M(I) and M(II); the six M(II) sites are preferentially occupied by the seven coordinated trivalent ions with Cs symmetry; while the other four M(I) sites are usually occupied by bivalent ions or the remaining trivalent ions with nine coordinations and C3 symmetry, respectively. Owing to the specific structure, apatite has great capacity to form solid solution and can accept several substitutes [3-5]. Among many synthetic apatite, the oxyapatite family are of practical interest as efficient laser-host materials and luminescence materials when doped with rare-earth ions [6,7], because of their high crystal field and excellent thermal, mechanical, and chemical properties [8]. It has been recognized that Ce3+ ions are good activators for phosphors because of their efficient photoluminescence from its parity allowed 5d–4f transitions. What’s more, the position of the lowest 5d band of Ce3+ ions is strongly influenced by host lattice selection, thus the emission color can be adjusted from ultraviolet to yellow [9]. However, the potential applications of the Ce3+ doped apatite phosphors are still limited because the emission often locates at shorter wavelength, as reported for Mg2Y8(SiO4)6O2: Ce3+ (395 nm) [10], Ca5(PO4)3F: Ce3+ (432 nm) [11]
and Ca5La5(SiO4)3(PO4)3O2: Ce3+ (385 nm) [12], etc. Till now, there has been few r
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