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

Abstract

Stannate-based pyrochlore-type red phosphors CaGd(1-x)SnNbO7:xEu(3+), Ca(1-y)Sr(y)Gd(1-x)SnNbO7:xEu(3+), and Ca(0.8-x)Sr0.2GdSnNbO(7+δ): xEu(3+) 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 Eu(3+) 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 Eu(3+) emission due to magnetic dipole transition ((5)D0-(7)F1 MD) is modified with the increase in europium concentration in the quaternary pyrochlore red phosphors. (5)D0-(7)F1 MD transition splitting is not observable for low Eu(3+) 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 Eu(3+) ions when it replaces a metal ion having lower oxidation state such as Ca(2+) was also investigated. The relative intensities of A1g (∼500 cm(-1)) and F2g (∼330 cm(-1)) Raman vibrational modes get inverted when Eu(3+) ions replaces Ca(2+) ions instead of Gd(3+) 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 Eu(3+) in Ca0.7Sr0.2GdSnNbO7+δ:0.1Eu(3+) phosphor is greatly strengthened the charge transfer band and (7)F0-(5)L6 transition intensities than that of the Ca0.8Sr0.2Gd0.9SnNbO7:0.1Eu(3+) phosphor. Our results suggest that the photoluminescence properties can be enhanced by simple compositional adjustments in the quaternary pyrochlore-type red phosphors.

Site selective substitution and its influence on photoluminescence properties of Sr0.8Li0.2Ti0.8Nb0.2O3:Eu3+ phosphors

“…44 The band for O 2p / Eu 4f and O 2p / Nb 4d charge transfer transitions usually lie in the regions 250-300 and 250-310 nm. 4,43 The observed CTB with low intensity in the region 350 to 450 nm is in agreement with the other reports on SrTiO 3 :Eu based phosphors. 11,45 Similarly, for CaTiO 3 :Eu phosphor systems also a low intense CTB was observed in the region 370-410 nm, overlapped with f-f transitions.…”

Crystal-Site Engineering Control for the Reduction of Eu3+ to Eu2+ in CaYAlO4: Structure Refinement and Tunable Emission Properties

“…13,52 In addition, the Raman spectrum, which is more sensitive to the cluster ordering, has been conducted to reveal the local ordering, deformation about site symmetry, etc. 53,54 As shown in Supporting Information Figure S5, the main phonon modes basically do not change with the introduction of Si 4+ − Ca 2+ , which is consistent with the XRD results. Furthermore, due to the fact that Ca 2+ site is surrounded compactly by AlO 6 octahedrons, the 27 Al solid-state NMR spectra of CYASO:Eu (x = 0, 0.15, and 0.30) samples have been performed to further clarify the effect of incorporating Si 4+ −Ca 2+ on Ca 2+ site as displayed in Figure 4.…”

Structural and photoluminescence properties of stannate based displaced pyrochlore-type red phosphors: Ca3−xSn3Nb2O14:xEu3+

“…28 Based on the D 3d symmetry at A site, the MD transition is expected to have splitting into two as observed in the normal pyrochlore. 26,29 In contrast to this, no such splitting is observed in the present displaced pyrochlore system. As discussed in the earlier literature, [9][10][11]30 displaced pyrochlores exhibit substantial displacive disorder in the A 2 O′ subnetwork.…”