Correlated N/O anion orders in melilite phosphors.

The N/O anion distributions in the melilite-type phosphor host material Y 2 Si 3 O 3 N 4 and a Ce-doped sample Y 1.5 Ce 0.5 Si 3 O 3 N 4 have been determined from powder neutron diffraction. Both materials have a highly ordered N/O distribution that is not changed significantly by the disorder introduced by Ce doping. This distribution evidences the presence of SiN 3 O and SiN 2 O 2 tetrahedra and although these are not fully long range-ordered, local structural correlations follow simple connectivity rules that lead to an estimated residual molar entropy of R ln3. A broad range of N/O environments is found around 8-coordinate Y(Ce) sites which is expected to broaden their spectroscopic features. SiN 3 O groups in the melilite-type phosphor host material Y 2 Si 3 O 3 N 4 and a Ce-doped sample Y 1.5 Ce 0.5 Si 3 O 3 N 4 have local structural correlations that follow simple connectivity rules and lead to an estimated residual molar entropy of R ln3. Image 1 [ABSTRACT FROM AUTHOR]