Site and local structure of activator Eu2+ in phosphor Ca10-x(PO4)6Cl2:xEu2+

The site and local structure of activator Eu2+ in phosphor Ca10-x(PO4)(6)Cl-2:xEu(2+) is investigated by experiment measurements, first-principle calculations and XAFS simulations. From first-principle calculations, the local structure [bond length L(M-O) <= R(M2+)+R(O2-)] of host shows a significant deformation (expansion) when Ca2+ is substituted by Eu2+, and Eu2+ should prefer 6h site to 4f site in the host. The d -> f emission of Eu2+ at 4f site should show a longer wavelength than that of Eu2+ at 6h site. The XAFS measurement and simulations suggest that the Eu2+ in our Ca-9.9(PO4)(6)Cl-2:0.1Eu(2+) sample mainly locates at 6h site. In the emission spectrum, two emission profiles of Ca-9.9(PO4)(6)Cl-2:0.1Eu(2+) sample are obtained and assigned. The major one (2.71 eV approximate to 456 nm) should be the emission of Eu2+ at 6h site. The minor one (2.61 eV approximate to 465 nm) should be that of Eu2+ at 4f site. (C) 2013 Elsevier Inc. All rights reserved.