Relationship between the structural characteristics and photoluminescent properties of LnEuTi2O7 (Ln=Gd and Y) pyrochlores

Mixed pyrochlore oxides LnEuTi2O7 (Ln=Gd and Y) were prepared by solid-state reaction and their structures have been confirmed and characterized using X-ray powder diffraction (XRD), Raman, FT-IR and photoluminescence (PL) techniques. Raman spectra and X-ray diffraction patterns revealed the formation of pure oxides after sintering at 1200 °C. These compounds were crystallized in a pyrochlore structure A2B2O7 in a cubic lattice with an Fd3m space group and their refined lattice parameters were in the range of 10.197(6)-10.157(4) Å for GdEuTi2O7 and YEuTi2O7, respectively. The X-ray Rietveld analysis indicated that Eu3+ ions were located in the A3+ site with inversion symmetry. The IR active bands, characteristic of the A and B sites of a pyrochlore compound, were detected by infrared spectroscopy due to their metal-oxygen bonds. The samples luminescence properties were analyzed by measuring the excitation and emission spectra. Results indicated that the as-prepared samples showed a strong emission of Eu3+ under their radiation of 325 nm. For LnEuTi2O7 oxides, the orange emission at 589 nm was the strongest, which corresponded to the magnetic dipole transition 5D0-7F1 due to an energy transfer from hosts. However, the red emissions 5D0-7F2 were very weak because electronic dipole transitions are parity forbidden. This fact also confirmed that the Eu3+ ions were located in the sites with the inversion center.