EU3+ LUMINESCENCE - A SPECTRAL PROBE IN M(5)(PO4)(3)X APATITES (M=CA OR SR X=F-, CL-, BR- OR OH-)

EU(3+) luminescence is of special importance as a spectral probe apart from its application in phosphor materials. This is possible for the reason that Eu3+ has several structure-dependent transitions enabling one to gain insight about the site that it occupies in a given host. On this basis we have attempted to explore the different cationic sites present in the apatite system. In fluoroapatites, EU(3+) predominantly occupies M(II) sites, with the local symmetry becoming enhanced from C-1h to a tetragonal symmetry attributed to charge-compensating species. In addition to both kinds of site of the apatite system (M(I) and M(II)) occupied by EU(3+), we have observed the presence of a third kind of EU(3+), site. The observation of unusually strong D-5(0) -t F-7(0) emission of EU(3+) in fluoroapatites and bromoapatites has been explained. Also various results on the luminescence features of EU(3+) correlated with the structural details known are discussed.