STRUCTURAL AND OPTICAL-PROPERTIES OF THE SYSTEM (CA,SR,EU)(5)(PO4)(3)CL

Polycrystalline materials of the composition Sr5-x-yCaxEuy(PO4)(3)Cl w ith 0 less than or equal to x less than or equal to 4.99 and 0 less th an or equal to y less than or equal to 0.1 crystallize in the hexagona l crystal system. The space group is P6(3)/m. The alkaline earth ions occupy two different crystallographical sites. In addition to X-ray di ffraction measurements, the optical properties are studied at room tem perature. Moreover the emission spectra are measured at liquid nitroge n temperature. Refinement of the structure parameters is carried out u sing the Rietveld method. A varying calcium portion influences the lat tice constants a(0) and c(0) and therefore the luminescence of the sam ples. The luminescence arises from transitions between 4f(6)5d and 4f( 7) configurations of the Eu2+ ion.