13 research outputs found
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
Incommensurately modulated structures and luminescence properties of the <tex>Ag_{x}Sm_{(2-x)/3}WO_{4}$</tex> (x=0.286, 0.2) scheelites as thermographic phosphors
<tex>Ag_{1/8}Pr_{5/8}MoO_{4}:$</tex> an incommensurately modulated scheelite-type structure
Novel Red Phosphor of Gd<sup>3+</sup>, Sm<sup>3+</sup> co-Activated Ag<i><sub>x</sub></i>Gd<sub>((2−<i>x</i>)/3)−0.3−<i>y</i></sub>Sm<i><sub>y</sub></i>Eu<sup>3+</sup><sub>0.30</sub>☐<sub>(1−2<i>x</i>−2<i>y</i>)/3</sub>WO<sub>4</sub> 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
New molybdenum oxides <tex>Ag_{4}M_{2}Zr(MoO_{4})_{6}$</tex> (M=Mg, Mn, Co, Zn) with a channel-like structure
Luminescence property upgrading via the structure and cation changing in <tex>Ag_{x}Eu_{(2-x)/3}WO_{4}</tex>
Incommensurately Modulated Structures and Luminescence Properties of the Ag<sub><i>x</i></sub>Sm<sub>(2–<i>x</i>)/3</sub>WO<sub>4</sub> (<i>x</i> = 0.286, 0.2) Scheelites as Thermographic Phosphors
Ag<sup>+</sup> for Sm<sup>3+</sup> substitution in the scheelite-type
Ag<sub><i>x</i></sub>Sm<sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> 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 <sup>4</sup>G<sub>5/2</sub> → <sup>6</sup>H<sub><i>J</i></sub> (<i>J</i> = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm<sup>3+</sup> 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 <sup>4</sup>G<sub>5/2</sub> → <sup>6</sup>H<sub>9/2</sub> and <sup>4</sup>G<sub>5/2</sub> → <sup>6</sup>H<sub>7/2</sub> 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<sub><i>x</i></sub>Eu<sub>(2–<i>x</i>)/3</sub>WO<sub>4</sub> and Ag<sub><i>x</i></sub>Gd<sub>(2–<i>x</i>)/3–0.3</sub>Eu<sub>0.3</sub>WO<sub>4</sub>
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<sub><i>x</i></sub>Eu<sup>3+</sup><sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> and Ag<sub><i>x</i></sub>Gd<sub>(2−<i>x</i>)/3−0.3</sub>Eu<sup>3+</sup><sub>0.3</sub>□<sub>(1−2<i>x</i>)/3</sub>WO<sub>4</sub> (<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<sub><i>x</i></sub>Eu<sup>3+</sup><sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> (<i>x</i> = 0.286, 0.2) phases. The crystal structures
of the scheelite-based Ag<sub><i>x</i></sub>Eu<sup>3+</sup><sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> (<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<sub><i>x</i></sub>Eu<sup>3+</sup><sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> (<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<sub>2/3</sub>□<sub>1/3</sub>WO<sub>4</sub> and Gd<sub>0.367</sub>Eu<sub>0.30</sub>□<sub>1/3</sub>WO<sub>4</sub> 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 <sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>2</sub> transition of Eu<sup>3+</sup>. Concentration
dependence of the <sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>2</sub> emission for Ag<sub><i>x</i></sub>Eu<sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>WO<sub>4</sub> samples differs from the same dependence for the earlier
studied Na<sub><i>x</i></sub>Eu<sup>3+</sup><sub>(2–<i>x</i>)/3</sub>□<sub>(1–2<i>x</i>)/3</sub>MoO<sub>4</sub> (0 ≤ <i>x</i> ≤ 0.5) phases.
The intensity of the <sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>2</sub> 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 Eu<sup>3+</sup> emission under excitation of Eu<sup>3+</sup>(<sup>5</sup>L<sub>6</sub>) level (λ<sub>ex</sub> = 395 nm) increases more than 2.5 times
with the increasing Gd<sup>3+</sup> concentration from 0.2 (<i>x</i> = 0.5) to 0.3 (<i>x</i> = 0.2) in the Ag<sub><i>x</i></sub>Gd<sub>(2−<i>x</i>)/3−0.3</sub>Eu<sup>3+</sup><sub>0.3</sub>□<sub>(1−2<i>x</i>)/3</sub>WO<sub>4</sub>, after which it remains almost constant for
higher Gd<sup>3+</sup> concentrations