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