New triple molybdate and tungstate Na5Rb7Sc2(XO4)9 (X = Mo, W)

New compounds of the composition Na5Rb7Sc2(XO4)9 (X = Mo, W) were obtained via the ceramic technology. The sequences of chemical transformations occurring during the formation of these compounds were established, and their primary characterization was performed. Both Na5Rb7Sc2(XO4)9 (X = Mo, W) were found to melt incongruently at 857 K (X = Mo) and 889 K (X = W). They are isostructural to Ag5Rb7Sc2(XO4)9 (X = Mo, W), Na5Cs7Ln2(MoO4)9 (Ln = Tm, Yb, Lu) and crystallize in the trigonal crystal system (sp. gr. R32). The crystal structures were refined with the Rietveld method using the powder X-ray diffraction data. The thermal expansion of Na5Rb7Sc2(WO4)9 was studied by high-temperature powder X-ray diffraction; it was shown that this triple tungstate belongs to high thermal expansion materials

Novel Red Phosphor of Gd³⁺, Sm³⁺ co-Activated Ag<i>_x</i>Gd_{((2−<i>x</i>)/3)−0.3−<i>y</i>}Sm<i>_y</i>Eu³⁺_0.30☐_{(1−2<i>x</i>−2<i>y</i>)/3}WO₄ Scheelites for LED Lighting

Gd3+ and Sm3+ co-activation, the effect of cation substitutions and the creation of cation vacancies in the scheelite-type framework are investigated as factors influencing luminescence properties. AgxGd((2−x)/3)−0.3−ySmyEu3+0.3☐(1−2x)/3WO4 (x = 0.50, 0.286, 0.20; y = 0.01, 0.02, 0.03, 0.3) scheelite-type phases (AxGSyE) have been synthesized by a solid-state method. A powder X-ray diffraction study of AxGSyE (x = 0.286, 0.2; y = 0.01, 0.02, 0.03) shows that the crystal structures have an incommensurately modulated character similar to other cation-deficient scheelite-related phases. Luminescence properties have been evaluated under near-ultraviolet (n–UV) light. The photoluminescence excitation spectra of AxGSyE demonstrate the strongest absorption at 395 nm, which matches well with commercially available UV-emitting GaN-based LED chips. Gd3+ and Sm3+ co-activation leads to a notable decreasing intensity of the charge transfer band in comparison with Gd3+ single-doped phases. The main absorption is the 7F0 → 5L6 transition of Eu3+ at 395 nm and the 6H5/2 → 4F7/2 transition of Sm3+ at 405 nm. The photoluminescence emission spectra of all the samples indicate intense red emission due to the 5D0 → 7F2 transition of Eu3+. The intensity of the 5D0 → 7F2 emission increases from ~2 times (x = 0.2, y = 0.01 and x = 0.286, y = 0.02) to ~4 times (x = 0.5, y = 0.01) in the Gd3+ and Sm3+ co-doped samples. The integral emission intensity of Ag0.20Gd0.29Sm0.01Eu0.30WO4 in the red visible spectral range (the 5D0 → 7F2 transition) is higher by ~20% than that of the commercially used red phosphor of Gd2O2S:Eu3+. A thermal quenching study of the luminescence of the Eu3+ emission reveals the influence of the structure of compounds and the Sm3+ concentration on the temperature dependence and behavior of the synthesized crystals. Ag0.286Gd0.252Sm0.02Eu0.30WO4 and Ag0.20Gd0.29Sm0.01Eu0.30WO4, with the incommensurately modulated (3 + 1)D monoclinic structure, are very attractive as near-UV converting phosphors applied as red-emitting phosphors for LEDs

Incommensurately Modulated Structures and Luminescence Properties of the Ag_<i>x</i>Sm_{(2–<i>x</i>)/3}WO₄ (<i>x</i> = 0.286, 0.2) Scheelites as Thermographic Phosphors

Ag⁺ for Sm³⁺ substitution in the scheelite-type Ag_<i>x</i>Sm_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ tungstates has been investigated for its influence on the cation-vacancy ordering and luminescence properties. A solid state method was used to synthesize the <i>x</i> = 0.286 and <i>x</i> = 0.2 compounds, which exhibited (3 + 1)­D incommensurately modulated structures in the transmission electron microscopy study. Their structures were refined using high resolution synchrotron powder X-ray diffraction data. Under near-ultraviolet light, both compounds show the characteristic emission lines for ⁴G_5/2 → ⁶H_<i>J</i> (<i>J</i> = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm³⁺ ions in the range 550–720 nm, with the <i>J</i> = 9/2 transition at the ∼648 nm region being dominant for all photoluminescence spectra. The intensities of the ⁴G_5/2 → ⁶H_9/2 and ⁴G_5/2 → ⁶H_7/2 bands have different temperature dependencies. The emission intensity ratios (<i>R</i>) for these bands vary reproducibly with temperature, allowing the use of these materials as thermographic phosphors

New Solid Electrolyte Na 9 Al(MoO 4 ) 6 : Structure and Na + Ion Conductivity

International audienc

Luminescence Property Upgrading via the Structure and Cation Changing in Ag_<i>x</i>Eu_{(2–<i>x</i>)/3}WO₄ and Ag_<i>x</i>Gd_{(2–<i>x</i>)/3–0.3}Eu_0.3WO₄

The creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelite-type structure and luminescence properties. Ag_<i>x</i>Eu³⁺_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ and Ag_<i>x</i>Gd_{(2−<i>x</i>)/3−0.3}Eu³⁺_0.3□_{(1−2<i>x</i>)/3}WO₄ (<i>x</i> = 0.5–0) scheelite-type phases were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder synchrotron X-ray diffraction. Transmission electron microscopy also revealed the (3 + 1)­D incommensurately modulated character of Ag_<i>x</i>Eu³⁺_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ (<i>x</i> = 0.286, 0.2) phases. The crystal structures of the scheelite-based Ag_<i>x</i>Eu³⁺_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ (<i>x</i> = 0.5, 0.286, 0.2) red phosphors have been refined from high resolution synchrotron powder X-ray diffraction data. The luminescence properties of all phases under near-ultraviolet (n-UV) light have been investigated. The excitation spectra of Ag_<i>x</i>Eu³⁺_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ (<i>x</i> = 0.5, 0.286, 0.2) phosphors show the strongest absorption at 395 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. The excitation spectra of the Eu_2/3□_1/3WO₄ and Gd_0.367Eu_0.30□_1/3WO₄ phases exhibit the highest contribution of the charge transfer band at 250 nm and thus the most efficient energy transfer mechanism between the host and the luminescent ion as compared to direct excitation. The emission spectra of all samples indicate an intense red emission due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. Concentration dependence of the ⁵D₀ → ⁷F₂ emission for Ag_<i>x</i>Eu_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}WO₄ samples differs from the same dependence for the earlier studied Na_<i>x</i>Eu³⁺_{(2–<i>x</i>)/3}□_{(1–2<i>x</i>)/3}MoO₄ (0 ≤ <i>x</i> ≤ 0.5) phases. The intensity of the ⁵D₀ → ⁷F₂ emission is reduced almost 7 times with decreasing <i>x</i> from 0.5 to 0, but it practically does not change in the range from <i>x</i> = 0.286 to <i>x</i> = 0.200. The emission spectra of Gd-containing samples show a completely different trend as compared to only Eu-containing samples. The Eu³⁺ emission under excitation of Eu³⁺(⁵L₆) level (λ_ex = 395 nm) increases more than 2.5 times with the increasing Gd³⁺ concentration from 0.2 (<i>x</i> = 0.5) to 0.3 (<i>x</i> = 0.2) in the Ag_<i>x</i>Gd_{(2−<i>x</i>)/3−0.3}Eu³⁺_0.3□_{(1−2<i>x</i>)/3}WO₄, after which it remains almost constant for higher Gd³⁺ concentrations