Eu3+luminescence: A spectral probe in M5(PO4)3X 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 Eu 3+ 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 5 D 0 to 7 F 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.