Synthesis, structure and luminescence properties of the europium–containing NASICON type phosphates

Synthesis process, structure and luminescent properties of NASICON (Na super ionic conductor) type phosphates doped with europium have been investigated for the Na1-xEu0.33xTi2(PO4)3 series. The samples were synthesized via Pechini technique. Differential thermal analysis of the reaction mixtures was used to choose the optimal scheme for the thermal treatment of the phosphates. The obtained samples were studied by means of X-ray powder diffraction (including Rietveld structure refinement), Infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was shown that the phosphates with 0 ≤ x ≤ 0.1 were crystallized in the space group $$R\overline 3 c$$ , while the phosphates with 0.2 ≤ x ≤ 1.0 characterized by the space group $$R\overline 3$$ . Photoluminescence emission spectra of the phosphates Na1-xEu0.33xTi2(PO4)3 showed typical emission bands of Eu3+ ions, due to 5D0 → 7FJ transitions. The intensity of the emission bands rises with the concentration of europium up to x = 0.7 (Na0.3Eu0.23Ti2(PO4)3), while a further increase of x results into concentration quenching. Na0.5Eu0.167Ti2(PO4)3 structure and Na1-xEu0.33xTi2(PO4)3 photoluminescence emission spectra