Influence of Cation Substitution and Activator Site Exchange on the Photoluminescence Properties of Eu3+-Doped Quaternary Pyrochlore Oxides

• Published in: Inorganic chemistry Vol. 52; no. 23; pp. 13304 - 13313
• Main Authors: Mahesh, S. K, Rao, P. Prabhakar, Thomas, Mariyam, Francis, T. Linda, Koshy, Peter
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.12.2013
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic401802s

Stannate-based pyrochlore-type red phosphors CaGd1–x SnNbO7:xEu3+, Ca1–y Sr y Gd1–x SnNbO7:xEu3+, and Ca0.8–x Sr0.2GdSnNbO7+δ: xEu3+ were prepared via conventional solid-state method. Influence of cation substitution and activator site control on the photoluminescence properties of these phosphors are elucidated using powder X-ray diffraction, Rietveld analysis, Raman spectrum analysis, and photoluminescence excitation and emission spectra. The Eu3+ luminescence in quaternary pyrochlore lattice exemplifies as a very good structural probe for the detection of short-range disorder in the lattice, which otherwise is not detected by normal powder X-ray diffraction technique. The Eu3+ emission due to magnetic dipole transition (5D0–7F1 MD) is modified with the increase in europium concentration in the quaternary pyrochlore red phosphors. 5D0–7F1 MD transition splitting is not observable for low Eu3+ doping because of the short-range disorder in the pyrochlore lattice. Appearance of narrow peaks in Raman spectra confirms that short-range disorder in the crystal lattice disappears with progressive europium doping. By using Sr as a network modifier ion in place of Ca we were able to increase the f–f transition intensities and europium quenching concentration. The influence of effective positive charge of the central Eu3+ ions when it replaces a metal ion having lower oxidation state such as Ca2+ was also investigated. The relative intensities of A1g (∼500 cm–1) and F2g (∼330 cm–1) Raman vibrational modes get inverted when Eu3+ ions replaces Ca2+ ions instead of Gd3+ as trivalent europium ions can attract the electron cloud of oxygen ions strongly in comparison with divalent calcium ions. The influence of positive charge effect of Eu3+ in Ca0.7Sr0.2GdSnNbO7+δ:0.1Eu3+ phosphor is greatly strengthened the charge transfer band and 7F0-5L6 transition intensities than that of the Ca0.8Sr0.2Gd0.9SnNbO7:0.1Eu3+ phosphor. Our results suggest that the photoluminescence properties can be enhanced by simple compositional adjustments in the quaternary pyrochlore-type red phosphors.