3 research outputs found
La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> – A Yellow Phosphor with an Unprecedented Tetrahedra Network Structure Investigated by Combination of Electron Microscopy and Synchrotron X‑ray Diffraction
Due to the relationship between structure
and luminescence properties,
detailed crystal structure determination for microcrystalline phosphors
is necessary for a profound understanding of materials properties.
The yellow phosphor La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> (λ<sub>max</sub> = 578 nm; fwhm ∼4700
cm<sup>–1</sup>) was characterized by a combination of transmission
electron microscopy (TEM) and synchrotron microfocus diffraction as
only agglomerates of crystals with a maximum size of a few μm
could be obtained yet. La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> was synthesized from LaF<sub>3</sub>, LaÂ(NH<sub>2</sub>)<sub>3</sub>, BaH<sub>2</sub>, SiÂ(NH)<sub>2</sub>, and CeF<sub>3</sub> in a radio frequency furnace. It crystallizes
in space group <i>Pmn</i>2<sub>1</sub> (no. 31) with <i>a</i> = 9.5505(8), <i>b</i> = 19.0778(16), <i>c</i> = 12.1134(9) Ã…, and <i>Z</i> = 8. Its interrupted
three-dimensional tetrahedra network contains <i>zehner</i> and <i>dreier</i> rings of vertex-sharing SiN<sub>4</sub> and SiN<sub>2</sub>O<sub>2</sub> tetrahedra. The crystal structure
was confirmed by high-resolution TEM and Z-contrast scanning TEM.
The element distribution was derived by bond-valence sum calculations.
The infrared spectrum proves the absence of N–H bonds
La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> – A Yellow Phosphor with an Unprecedented Tetrahedra Network Structure Investigated by Combination of Electron Microscopy and Synchrotron X‑ray Diffraction
Due to the relationship between structure
and luminescence properties,
detailed crystal structure determination for microcrystalline phosphors
is necessary for a profound understanding of materials properties.
The yellow phosphor La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> (λ<sub>max</sub> = 578 nm; fwhm ∼4700
cm<sup>–1</sup>) was characterized by a combination of transmission
electron microscopy (TEM) and synchrotron microfocus diffraction as
only agglomerates of crystals with a maximum size of a few μm
could be obtained yet. La<sub>3</sub>BaSi<sub>5</sub>N<sub>9</sub>O<sub>2</sub>:Ce<sup>3+</sup> was synthesized from LaF<sub>3</sub>, LaÂ(NH<sub>2</sub>)<sub>3</sub>, BaH<sub>2</sub>, SiÂ(NH)<sub>2</sub>, and CeF<sub>3</sub> in a radio frequency furnace. It crystallizes
in space group <i>Pmn</i>2<sub>1</sub> (no. 31) with <i>a</i> = 9.5505(8), <i>b</i> = 19.0778(16), <i>c</i> = 12.1134(9) Ã…, and <i>Z</i> = 8. Its interrupted
three-dimensional tetrahedra network contains <i>zehner</i> and <i>dreier</i> rings of vertex-sharing SiN<sub>4</sub> and SiN<sub>2</sub>O<sub>2</sub> tetrahedra. The crystal structure
was confirmed by high-resolution TEM and Z-contrast scanning TEM.
The element distribution was derived by bond-valence sum calculations.
The infrared spectrum proves the absence of N–H bonds
Puzzling Intergrowth in Cerium Nitridophosphate Unraveled by Joint Venture of Aberration-Corrected Scanning Transmission Electron Microscopy and Synchrotron Diffraction
Thorough
investigation of nitridophosphates has rapidly accelerated
through development of new synthesis strategies. Here we used the
recently developed high-pressure metathesis to prepare the first rare-earth
metal nitridophosphate, Ce<sub>4</sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35</sub>, with a high degree of condensation >1/2. Ce<sub>4</sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35</sub> consists of an
unprecedented
hexagonal framework of PN<sub>4</sub> tetrahedra and exhibits blue
luminescence peaking at 455 nm. Transmission electron microscopy (TEM)
revealed two intergrown domains with slight structural and compositional
variations. One domain type shows extremely weak superstructure phenomena
revealed by atomic-resolution scanning TEM (STEM) and single-crystal
diffraction using synchrotron radiation. The corresponding superstructure
involves a modulated displacement of Ce atoms in channels of tetrahedra
6-rings. The displacement model was refined in a supercell as well
as in an equivalent commensurate (3 + 2)-dimensional description in
superspace group <i>P</i>6<sub>3</sub>(α, β,
0)Â0Â(−α – β, α, 0)Â0. In the second
domain type, STEM revealed disordered vacancies of the same Ce atoms
that were modulated in the first domain type, leading to sum formula
Ce<sub>4–0.5<i>x</i></sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35–1.5<i>x</i></sub>O<sub>1.5<i>x</i></sub> (<i>x</i> ≈ 0.72) of the average structure.
The examination of these structural intricacies may indicate the detection
limit of synchrotron diffraction and TEM. We discuss the occurrence
of either Ce displacements or Ce vacancies that induce the incorporation
of O as necessary stabilization of the crystal structure