Structural approach and luminescence properties of La1/6Pb1/3Zr2(PO4)17/6(SiO4)1/6:: Eu3+

Rare earth phosphosilicates (Li1-xEux)(1/6)Pb1/3Zr2(PO4)(17/6) (SiO4)(1/6) 0 less than or equal to x less than or equal to 1 have been synthesized via a sol-gel route, The powder X-ray diffraction has been analyzed with the Nasicon-type structure. The Rietveld analysis of the structure performed in space group R (3) over bar shows a statistical distribution of ions La3+ Eu3+, and Pb2+ over the positions 3a (occupation 10%) and 3b (occupation 90%) of the so-called hll site, In agreement with these results, the Eu3+ luminescence analysis in these phases exhibits two sites for Eu3+, both are noncentrosymmetric, revealing a local disorder in the compounds, which is also supported by the inhomogeneous broadening of the emission lines. The luminescence characteristics of this family of silicates have been investigated for various x values. Under excitation at 254 nm, the distinct emissions of Pb2+ and of Eu3+ are observed, The excitation of Eu3+ ions occurs directly via the charge transfer state or after Pb2+ --> Eu3+ energy transfer. Concentration quenching of the Eu3+ emission is also investigated, (C) 1999 Academic Press.