New insight in the structure-luminescence relationships of Ca9Eu(PO4)7

The double phosphate Ca9Eu(PO4)(7), obtained by solid state reaction, was found to be isotypic with Ca-3(PO4)(2), with space group R3c and unit cell parameters a = 10.4546(1)angstrom, c = 37.4050(3)angstrom, V = 3540.67(9)angstrom(3), Z = 6. The structure parameters refined using the Rietveld method showed that europium shares positions M1, M2 and M3 with calcium, contradicting previously published Mossbauer results. Low temperature luminescence under selective excitation of Eu3+ in Ca9Y1-xEux(PO4)(7) and in CagEu(PO4)(7) samples was studied, confirming the Eu3+ distribution into these sites. At 10K, D-5(0) -> F-7(0) emission lines of Eu3+ were observed at 578.5, 579.5, 580.1 nm for the M3, M1 and M2 sites, respectively. High temperature X-ray powder diffraction evidenced a second-order phase transition around 573 degrees C. (C) 2009 Elsevier Inc. All rights reserved.