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
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>Â =Â 3, 4, 5): crystal structure, spectroscopic and thermal properties
<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
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
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
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
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>CaÂ(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup>, and the cyan Ba<sub>2</sub>CaÂ(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>Â(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> Phosphor for Near-UV Pumped White Light-Emitting Devices
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>Â(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>Â(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>
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
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
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)
Ã…, <i>V</i> = 1188.123(8) Ã…<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