13 research outputs found

    Structural and Luminescence Properties of Yellow-Emitting NaScSi<sub>2</sub>O<sub>6</sub>:Eu<sup>2+</sup> Phosphors: Eu<sup>2+</sup> Site Preference Analysis and Generation of Red Emission by Codoping Mn<sup>2+</sup> for White-Light-Emitting Diode Applications

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    The structural properties of clinopyroxene NaScSi<sub>2</sub>O<sub>6</sub> have been investigated using the X-ray powder diffraction refinement, and the luminescence properties of Eu<sup>2+</sup> and Eu<sup>2+</sup>/Mn<sup>2+</sup>-activated NaScSi<sub>2</sub>O<sub>6</sub> have been studied to explore the new materials for phosphor-converted white light ultraviolet light-emitting diodes (UV-LEDs). Eu<sup>2+</sup> was introduced into the NaScSi<sub>2</sub>O<sub>6</sub> host in the reducing atmosphere, and the preferred crystallographic positions of the Eu<sup>2+</sup> ions were determined based on the different structural models of the NaScSi<sub>2</sub>O<sub>6</sub> host. The as-obtained NaScSi<sub>2</sub>O<sub>6</sub>:Eu<sup>2+</sup> phosphor shows greenish yellow emission with the broad-band peak at 533 nm, and efficient energy transfer (ET) takes place between Eu<sup>2+</sup> and Mn<sup>2+</sup> in NaScSi<sub>2</sub>O<sub>6</sub>, leading to a series of color-tunable phosphors emitting at 533 and 654 nm for the designed NaScSi<sub>2</sub>O<sub>6</sub>:Eu<sup>2+</sup>,Mn<sup>2+</sup> phosphors under excitation at 365 nm. The ET mechanism of Eu<sup>2+</sup> and Mn<sup>2+</sup> has also been evaluated. We have demonstrated that NaScSi<sub>2</sub>O<sub>6</sub>:Eu<sup>2+</sup> and NaScSi<sub>2</sub>O<sub>6</sub>:Eu<sup>2+</sup>,Mn<sup>2+</sup> materials exhibit great potential to act as the effective phosphors for UV-LEDs

    Hydrates [Na<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub>](2-thiobarbiturate)<sub>2</sub> (<i>x</i> = 3, 4, 5): crystal structure, spectroscopic and thermal properties

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    <p>The hydrates [Na<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>(Htba)<sub>2</sub>] (<b>1</b>) and [Na<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>(Htba)<sub>2</sub>] (<b>2</b>), where H<sub>2</sub>tba is 2-thiobarbituric acid, were obtained under different thermal conditions from aqueous solutions and were structurally characterized. The molecular and supramolecular structures were compared to the known structure of [Na<sub>2</sub>(H<sub>2</sub>O)<sub>5</sub>(Htba)<sub>2</sub>] (<b>3</b>). In polymeric <b>1</b>–<b>3</b>, the Htba<sup>−</sup> ions are linked to Na<sup>+</sup> through O and S forming octahedra. The decrease of the number of coordination water molecules led to an increase of the total number of bridge ligands (μ<sub>2</sub>-H<sub>2</sub>O, Htba<sup>−</sup>) and a change of the Htba<sup>−</sup> coordination. These factors induced higher distortion of the octahedra. It was assumed that hydrates, with a different number of coordinated water molecules, are more probable when the central metal has weaker bonds with O water molecules and with other ligands. The net topologies of <b>1</b>–<b>3</b> were compared. Thermal decomposition and IR spectra were analyzed for <b>1</b> and <b>2</b>.</p

    Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

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    Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, the substitution of Ca<sup>2+</sup> by Sr<sup>2+</sup> induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO<sub><i>n</i></sub>–Ca<sub>9</sub> and EuO<sub><i>n</i></sub>–Ca<sub>9–<i>x</i></sub>Sr<sub><i>x</i></sub> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

    Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

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    Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, the substitution of Ca<sup>2+</sup> by Sr<sup>2+</sup> induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO<sub><i>n</i></sub>–Ca<sub>9</sub> and EuO<sub><i>n</i></sub>–Ca<sub>9–<i>x</i></sub>Sr<sub><i>x</i></sub> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

    Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

    No full text
    Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, the substitution of Ca<sup>2+</sup> by Sr<sup>2+</sup> induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO<sub><i>n</i></sub>–Ca<sub>9</sub> and EuO<sub><i>n</i></sub>–Ca<sub>9–<i>x</i></sub>Sr<sub><i>x</i></sub> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

    Discovery of New Solid Solution Phosphors via Cation Substitution-Dependent Phase Transition in M<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (M = Ca/Sr/Ba) Quasi-Binary Sets

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    The cation substitution-dependent phase transition was used as a strategy to discover new solid solution phosphors and to efficiently tune the luminescence property of divalent europium (Eu<sup>2+</sup>) in the M<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> (M = Ca/Sr/Ba) quasi-binary sets. Several new phosphors including the greenish-white SrCa<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, the yellow Sr<sub>2</sub>Ca­(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, and the cyan Ba<sub>2</sub>Ca­(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> were reported, and the drastic red shift of the emission toward the phase transition point was discussed. Different behavior of luminescence evolution in response to structural variation was verified among the three M<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> joins. Sr<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and Ba<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> form a continuous isostructural solid solution set in which Eu<sup>2+</sup> exhibits a similar symmetric narrow-band blue emission centered at 416 nm, whereas Sr<sup>2+</sup> substituting Ca<sup>2+</sup> in Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> induces a composition-dependent phase transition and the peaking emission gets red shifted to 527 nm approaching the phase transition point. In the Ca<sub>3–<i>x</i></sub>Ba<sub><i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> set, the validity of crystallochemical design of phosphor between the phase transition boundary was further verified. This cation substitution strategy may assist in developing new phosphors with controllably tuned optical properties based on the phase transition

    New Yellow-Emitting Whitlockite-type Structure Sr<sub>1.75</sub>Ca<sub>1.25</sub>­(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> Phosphor for Near-UV Pumped White Light-Emitting Devices

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    New compound discovery is of interest in the field of inorganic solid-state chemistry. In this work, a whitlockite-type structure Sr<sub>1.75</sub>Ca<sub>1.25</sub>­(PO<sub>4</sub>)<sub>2</sub> newly found by composition design in the Sr<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>–Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> join was reported. Crystal structure and luminescence properties of Sr<sub>1.75</sub>Ca<sub>1.25</sub>­(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> were investigated, and the yellow-emitting phosphor was further employed in fabricating near-ultraviolet-pumped white light-emitting diodes (w-LEDs). The structure and crystallographic site occupancy of Eu<sup>2+</sup> in the host were identified via X-ray powder diffraction refinement using Rietveld method. The Sr<sub>1.75</sub>Ca<sub>1.25</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> phosphors absorb in the UV–vis spectral region of 250–430 nm and exhibit an intense asymmetric broadband emission peaking at 518 nm under λ<sub>ex</sub> = 365 nm which is ascribed to the 5d–4f allowed transition of Eu<sup>2+</sup>. The luminescence properties and mechanism are also investigated as a function of Eu<sup>2+</sup> concentration. A white LED device which is obtained by combining a 370 nm UV chip with commercial blue phosphor and the present yellow phosphor has been fabricated and exhibit good application properties

    Synthesis, Crystal Structure, and Optical Gap of Two-Dimensional Halide Solid Solutions CsPb<sub>2</sub>(Cl<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>5</sub>

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    Exploring new perovskite-related solid-state materials and the investigating composition-dependent structural and physical properties are highly important for advanced functional material development. Herein, we present the successful hydrothermal synthesis of tetragonal CsPb<sub>2</sub>Cl<sub>5</sub> and the anion-exchange phase formation of CsPb<sub>2</sub>(Cl<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>5</sub> (<i>x</i> = 0–1) solid solutions. The CsPb<sub>2</sub>(Cl<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>5</sub> crystal structures, which crystallize in the tetragonal system, space group <i>I</i>4/<i>mcm</i>, with parameters similar to those of CsPb<sub>2</sub>Cl<sub>5</sub>, have been determined by Rietveld analysis. The optical band gap was obtained by UV–vis spectroscopy, and the band structure was further calculated by the full-potential method within the generalized gradient approximation. It was revealed that the band gap in CsPb<sub>2</sub>(Cl<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>5</sub> solid solutions can be tuned over the range of 4.5–3.8 eV by anion substitution

    Pressure-Stimulated Synthesis and Luminescence Properties of Microcrystalline (Lu,Y)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> Garnet Phosphors

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    The Lu<sub>2.98</sub>Ce<sub>0.01</sub>Y<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> and Y<sub>2.99</sub>Ce<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> phosphors were synthesized by solid state reaction at temperature 1623 K and pressure 1.5 × 10<sup>7</sup> Pa in (95% N<sub>2</sub> + 5% H<sub>2</sub>) atmosphere. Under the conditions, the compounds crystallize in the form of isolated euhedral partly faceted microcrystals ∼19 μm in size. The crystal structures of the Lu<sub>2.98</sub>Ce<sub>0.01</sub>Y<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> and Y<sub>2.99</sub>Ce<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> garnets have been obtained by Rietveld analysis. The photoluminescence (PL) and X-ray excited luminescence (XL) spectra obtained at room temperature indicate broad asymmetric bands with maxima near 519 and 540 nm for Y<sub>2.99</sub>Ce<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> and Lu<sub>2.98</sub>Ce<sub>0.01</sub>Y<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub>, respectively. The light source was fabricated using the powder Lu<sub>2.98</sub>Ce<sub>0.01</sub>Y<sub>0.01</sub>Al<sub>5</sub>O<sub>12</sub> phosphor and commercial blue-emitting n-UV LED chips (λ<sub>ex</sub> = 450 nm). It is found that the CIE chromaticity coordinates are (<i>x</i> = 0.388, <i>y</i> = 0.563) with the warm white light emission correlated color temperature (CCT) of 6400 K and good luminous efficiency of 110 lm/W

    Synthesis, Structural, Magnetic, and Electronic Properties of Cubic CsMnMoO<sub>3</sub>F<sub>3</sub> Oxyfluoride

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    A powder sample of CsMnMoO<sub>3</sub>F<sub>3</sub> oxyfluoride has been prepared by solid state synthesis. The pyrochlore-related crystal structure of CsMnMoO<sub>3</sub>F<sub>3</sub> has been refined by the Rietveld method at <i>T</i> = 298 K (space group <i>Fd-</i>3<i>m</i>, <i>a</i> = 10.59141(4) Å, <i>V</i> = 1188.123(8) Å<sup>3</sup>; <i>R</i><sub>B</sub> = 3.44%). The stability of the cubic phase has been obtained over the temperature range <i>T</i> = 110–293 K by heat capacity measurements. Magnetic properties have been measured over the range of <i>T</i> = 2–300 K. The electronic structure of CsMnMoO<sub>3</sub>F<sub>3</sub> has been evaluated by X-ray photoelectron spectroscopy. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and wide comparison with related oxides and fluorides. The competition between O<sup>2–</sup> and F<sup>–</sup> ions for metal valence electrons has been found
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