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

Polycrystalline materials of the composition Sr5-yEuy(PO4)(3)Cl1-xBrx with 0 less than or equal to x less than or equal to 1 and 0 less than or equal to y less than or equal to 0.05 were prepared by solid state reaction. The crystal structure, optical properties at room temperatu re, and the emission spectra of the mixed crystals at liquid nitrogen temperature are investigated. The structure parameters are refined usi ng Rietveld profile refinement procedures. The space group of the mate rials is P6(3)/m. The lattice constants a(0) and c(0) increase with ri sing bromide content in the samples. The emission band due to transiti ons between 4f(6)5d and 4f(7) configurations of the Eu2+ ions occupyin g 6h positions of the unit cell and the main excitation band are shift ed to lower energies. This shifting is explained by mutual deformation of the Br- ions. The fluorescence lifetime is independent of the brom ide content in the mixed crystals.