Ba3Ga3N5 - A Novel Host Lattice for Eu2+ - Doped Luminescent Materials with Unexpected Nitridogallate Substructure

The alkaline earth nitridogallate Ba3Ga3N5 was synthesized from the elements in a sodium flux at 760°C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba3Ga3N5 (space group C2/c (No. 15), a = 16.801(3), b = 8.3301(2), c = 11.623(2) Å, β = 109.92 (3)°, Z = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN4 tetrahedra, each sharing two edges and at least one corner with neighboring GaN4 units. There are three Ba2+ sites with coordination numbers six or eight, respectively, and one Ba2+ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu2+ - doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm−1). Ba3Ga3N5 is the first nitridogallate for which parity allowed broadband emission due to Eu2+ - doping has been found. The electronic structure of both Ba3Ga3N5 as well as isoelectronic but not isostructural Sr3Ga3N5 was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr3Ga3N5 and 1.46 eV for Ba3Ga3N5

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

Can accurate Pb isotopic compositions be determined on single fluid inclusions?

ISSN:0016-7037ISSN:1872-953

Tellurium isotopic composition of the early solar system - A search for effects resulting from stellar nucleosynthesis, ¹²⁶Sn decay and mass- independent fractionation

New precise Te isotope data acquired by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) are presented for selected extraterrestrial and terrestrial materials. Bulk samples of carbonaceous, ordinary and enstatite chondrites as well as the metal and sulfide phases of iron meteorites were analyzed to search for nucleosynthetic isotope anomalies and to find evidence of formerly live 126Sn, which decays to 126Te with a half-life of 234,500 yr. None of the meteorites show evidence of mass dependent Te isotope fractionations larger than 2‰ for δ 126/128Te. Following internal normalization of the data to 125Te/128Te, the Te isotope ratios of all analyzed meteorites were found to be identical to a terrestrial standard, within uncertainties. This provides evidence that the regions of the solar disk that were sampled during accretion of the meteorite parent bodies were well mixed and homogeneous on a large scale, with respect to Te isotopes. The data acquired for bulk carbonaceous chondrites indicate that the initial 126Sn/ 118Sn ratio of the solar system was -5, but this is dependent on the assumption that no redistribution of Sn and Te occurred since the start of the solar system. Five Archean sedimentary sulfides that display both mass dependent and mass-independent isotope effects for S yield internally normalized Te isotope data, which indicate that mass-independent Te isotope effects are absent. The mass dependent fractionations in these samples are constrained to be less than ~1‰ for δ126/128Te

Ba₃Ga₃N₅A Novel Host Lattice for Eu²⁺-Doped Luminescent Materials with Unexpected Nitridogallate Substructure

The alkaline earth nitridogallate Ba₃Ga₃N₅ was synthesized from the elements in a sodium flux at 760 °C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba₃Ga₃N₅ (space group <i>C</i>2/<i>c</i> (No. 15), <i>a</i> = 16.801(3), <i>b</i> = 8.3301(2), <i>c</i> = 11.623(2) Å, β = 109.92(3)°, <i>Z</i> = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN₄ tetrahedra, each sharing two edges and at least one corner with neighboring GaN₄ units. There are three Ba²⁺ sites with coordination numbers six or eight, respectively, and one Ba²⁺ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu²⁺-doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm^–1). Ba₃Ga₃N₅ is the first nitridogallate for which parity allowed broadband emission due to Eu²⁺-doping has been found. The electronic structure of both Ba₃Ga₃N₅ as well as isoelectronic but not isostructural Sr₃Ga₃N₅ was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr₃Ga₃N₅ and 1.46 eV for Ba₃Ga₃N₅

Nontypical Luminescence Properties and Structural Relation of Ba₃P₅N₁₀X:Eu²⁺ (X = Cl, I): Nitridophosphate Halides with Zeolite-like Structure

The isotypic nitridophosphates Ba₃P₅N₁₀X (X = Cl, I) have been synthesized by high-temperature reaction under pressures between 1 and 5 GPa. The crystal structures of both compounds were solved and refined using single-crystal X-ray diffraction data. Accuracy of the structure determination as well as phase purity of the products were confirmed by Rietveld refinement and FTIR spectroscopy. The band gap values (4.0–4.3 eV) for the direct transitions were determined from UV–vis data using the Kubelka–Munk function and were confirmed by DFT calculations. Both compounds crystallize in the Ba₃P₅N₁₀Br structure type (space group <i>Pnma</i> (No. 62), <i>Z</i> = 8; Ba₃P₅N₁₀Cl, <i>a</i> = 12.5182(5) Å, <i>b</i> = 13.1798(5) Å, <i>c</i> = 13.7676(6) Å, <i>R</i>1 = 0.0214, <i>wR</i>2 = 0.0526; Ba₃P₅N₁₀I, <i>a</i> = 12.6311(7) Å, <i>b</i> = 13.2565(8) Å, <i>c</i> = 13.8689(8) Å, <i>R</i>1 = 0.0257, <i>wR</i>2 = 0.0586) with a tetrahedra network being analogous to the topology of the JOZ zeolite structure type. The crystal structure is built up of all-side vertex-sharing PN₄ tetrahedra leading to a zeolite-like framework with three-dimensional <i>achter</i>-ring channels containing alternately Ba and respective halide atoms. The condensed <i>dreier</i>-, <i>vierer</i>-, and <i>sechser</i>-rings form two different composite building units made up of 3⁴4²8⁶-cages. Upon being doped with Eu²⁺, the title compounds exhibit intriguing luminescence properties, which were compared with that of Ba₃P₅N₁₀Br:Eu²⁺. Upon excitation by near-UV light, nonsaturated color luminescence from multiple emission centers was observed in the orange (X = Cl) and cyan to amber (X = I) spectral range of the visible spectrum

Ca[LiAl₃N₄]:Eu²⁺A Narrow-Band Red-Emitting Nitridolithoaluminate

Ca­[LiAl₃N₄]:Eu²⁺ is an intriguing new narrow-band red-emitting phosphor material with potential for application in high-power phosphor-converted light-emitting diodes (pc-LEDs). With excitation by blue InGaN-based LEDs, the compound exhibits an emission maximum at 668 nm with a full width at half maximum of only 1333 cm^–1 (∼60 nm). Ca­[LiAl₃N₄]:Eu²⁺ was synthesized from Ca, LiAlH₄, LiN₃, AlF₃, and EuF₃ in weld-shut Ta ampules, and the structure was solved and refined on the basis of single-crystal X-ray diffraction data. After isotypical crystallization with Na­[Li₃SiO₄], the compound forms a highly condensed framework of AlN₄ and LiN₄ tetrahedra [<i>I</i>4₁/<i>a</i> (no. 88), <i>Z</i> = 16, <i>a</i> = 11.1600(16) Å, and <i>c</i> = 12.865(3) Å] and can thus by classified as a nitridolithoaluminate. Both types of polyhedra are connected to each other by common edges and corners, yielding a high degree of condensation, κ = 1. The Ca site is positioned in the center of <i>vierer</i> ring channels along [001] and coordinated in a cuboidal manner by eight N atoms. To validate the presence of Li, transmission electron microscopy (TEM) investigations employing electron energy-loss spectroscopy (EELS) were carried out. Furthermore, to confirm the electrostatic bonding interactions and the chemical composition, lattice energy calculations [Madelung part of lattice energy (MAPLE)] have been performed

Nitridomagnesosilicate Ba[Mg₃SiN₄]:Eu²⁺ and Structure–Property Relations of Similar Narrow-Band Red Nitride Phosphors

The nitridomagnesosilicate Ba­[Mg₃SiN₄] has been synthesized in an arc-welded Ta ampule. The crystal structure was solved and refined from single-crystal X-ray data and Rietveld refinement on the basis of powder X-ray diffraction data, revealing a distorted triclinic variant of the UCr₄C₄ structure type (space group <i>P</i>1̅ (no. 2), <i>Z</i> = 1, <i>a</i> = 3.451(1), <i>b</i> = 6.069(5), <i>c</i> = 6.101(4) Å, α = 85.200(7), β = 73.697(5), γ = 73.566(8)°, <i>R</i>_p = 0.0218, <i>R</i>_wp = 0.0290). The crystal structure of Ba­[Mg₃SiN₄] consists of a highly condensed network of (Mg,Si)­N₄ tetrahedra with Ba²⁺ centered inside <i>vierer</i> ring channels along [100] in a cuboidal coordination by N^3–. From UV/vis-reflectance data, a band gap of ∼4.0 eV was estimated. Doping with Eu²⁺ shows promising luminescence properties of λ_em = 670 nm with an fwhm ∼1970 cm^–1. Furthermore, anomalous luminescence phenomena, such as trapped-exciton emission, were identified and considered. Ba­[Mg₃SiN₄]:Eu²⁺ is a further narrow-band red-emitting phosphor and is discussed concerning the structure–property relations of recently reported Eu²⁺-doped nitrides with narrow-band red emission

Group (III) Nitrides <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca, Sr, Ba, Eu) and Ba[Mg₂Ga₂N₄]Structural Relation and Nontypical Luminescence Properties of Eu²⁺ Doped Samples

The isotypic nitridomagnesoaluminates <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca,Sr, Ba,Eu) as well as a novel nitridomagnesogallate Ba­[Mg₂Ga₂N₄] have been synthesized by high-temperature reactions in arc-welded tantalum ampules. The crystal structures were solved and refined using single-crystal X-ray diffraction or powder X-ray diffraction data, respectively. All compounds crystallize in the UCr₄C₄-structure type (space group <i>I</i>4/<i>m</i> (no. 87), <i>Z</i> = 2, Ca­[Mg₂Al₂N₄]: <i>a</i> = 8.0655(11), <i>c</i> = 3.2857(7) Å, <i>wR</i>2 = 0.085 Sr­[Mg₂Al₂N₄]: <i>a</i> = 8.1008(11), <i>c</i> = 3.3269(7) Å, <i>wR</i>2 = 0.084; Eu­[Mg₂Al₂N₄]: <i>a</i> = 8.1539(12), <i>c</i> = 3.3430(7) Å, <i>wR</i>2 = 0.033; Ba­[Mg₂Al₂N₄]: <i>a</i> = 8.2602(9), <i>c</i> = 3.43198(19) Å, <i>wR</i>p = 0.031; Ba­[Mg₂Ga₂N₄]: <i>a</i> = 8.3654(12), <i>c</i> = 3.4411(7) Å, <i>wR</i>2 = 0.031) forming highly condensed anionic networks of disordered (Al/Mg)­N₄ and (Ga/Mg)­N₄ units, connected to each other by common edges and corners. The <i>M</i>²⁺ site is centered in <i>vierer</i> ring channels along [001] and coordinated in a cuboidal surrounding by N. Eu²⁺ doped samples of <i>M</i>[Mg₂Al₂N₄] (<i>M</i> = Ca,Sr,Ba) exhibit nontypical luminescence properties including trapped exciton emission in the red spectral region. These compounds widen the group of novel red-emitting materials such as Ca­[LiAl₃N₄]:Eu²⁺, Sr­[LiAl₃N₄]:Eu²⁺, or Sr­[Mg₃SiN₄]:Eu²⁺. Therefore, deep discussion of the observed anomalous luminescence is essential to understand the correlations between all these materials, which are fundamental to design narrow band luminescence of Eu²⁺ systems