Structural ordering studies of Nd3+ ion in eulytite-type M3Y(PO4)3 (M=Sr2+ or Ba2+) phosphates. First translucent ceramics from micro-crystalline cubic powders

Cubic phosphates of M3Y(PO4)3 (M = Sr2+ or Ba2+) from the eulytite family were studied as potential candidates for new optical polycrystalline ceramics showing transparency. Two series of Nd3+-doped Ba3Y(PO4)3 and Sr3Y(PO4)3 micro-powders were synthesized via solid-state reaction method. The correlation between their structure and spectroscopic properties and the effect of divalent Sr2+/Ba2+ cation creating a network was analyzed in detail. The crystal structure of Ba3Y(PO4)3 and Sr3Y(PO4)3 was solved ab initio based on their single crystals. Y3+ and Sr2+/Ba2+ ions do not share the same symmetry site and some slight distortion over crystallographic positions occupied by divalent and trivalent ions in the cationic sublattice was visible. Nd3+ reside at the Y3+ site but partial substitution of Ba2+ or Sr2+ cannot be excluded. The cationic and anionic disorder is reflected in spectroscopic properties. Nd3+ ion used as a structural probe shows multisite character and inhomogeneous distribution in both types of material, as determined using absorption spectroscopy at 4.2 K and laser-excited site-selective luminescence spectroscopy at 77 K. This is also clearly seen in excited state dynamics of 4F3/2 doublet analysis. A greater order for barium host lattice was observed. Also, the first un-doped translucent ceramics were obtained from micro-crystalline powders.