Narrow-Band Red Emission in the Nitridolithoaluminate Sr₄[LiAl₁₁N₁₄]:Eu²⁺

The new narrow-band red-emitting phosphor material Sr₄[LiAl₁₁N₁₄]:Eu²⁺ was synthesized by solid-state reaction using a tungsten crucible with a cover plate in a tube furnace. When excited with blue light (460 nm), it exhibits red fluorescence with an emission maximum at 670 nm and a full width at half-maximum of 1880 cm^–1 (∼85 nm). The crystal structure was solved and refined from single-crystal X-ray diffraction data. This new compound from the group of the nitridolithoaluminates crystallizes in the orthorhombic space group <i>Pnnm</i> (No. 58) with the following unit-cell parameters: <i>a</i> = 10.4291(7) Å, <i>b</i> = 10.4309(7) Å, and <i>c</i> = 3.2349(2) Å. Sr₄[LiAl₁₁N₁₄]:Eu²⁺ shows a pronounced tetragonal pseudo-symmetry. It consists of a framework of disordered (Al/Li)­N₄ and AlN₄ tetrahedra that are connected to each other by common corners and edges. Along the [001] direction, the tetrahedral network creates empty four-membered-ring channels as well as five-membered-ring channels, in which the Sr²⁺ cations are located

Magnesium Double Nitride Mg₃GaN₃ as New Host Lattice for Eu²⁺ Doping: Synthesis, Structural Studies, Luminescence, and Band-Gap Determination

The double nitride Mg₃GaN₃ and binary nitride Mg₃N₂ were synthesized from the elements by reaction with NaN₃ in a sodium flux. Reactions were carried out at 760 °C in welded shut tantalum ampules. Mg₃GaN₃ was obtained as single crystals (space group <i>R</i>3̅<i>m</i> (No. 166), <i>a</i> = 3.3939(5) Å and <i>c</i> = 25.854(5) Å, <i>Z</i> = 3, <i>R</i>1 = 0.0252, <i>wR</i>2 = 0.0616 for 10 refined parameters, 264 diffraction data points). This double nitride consists of an uncharged three-dimensional network of MgN₄ and mixed (Mg/Ga)­N₄ tetrahedra, which share common corners and edges. First-principles density functional theory (DFT) calculations predict Mg₃GaN₃ to have a direct band gap of 3.0 eV, a value supported by soft X-ray spectroscopy measurements at the N K-edge. Eu²⁺-doped samples show yellow luminescence when irradiated with UV to blue light (λ_max = 578 nm, full width at half maximum (fwhm) = 132 nm). Eu²⁺-doped samples of Mg₃N₂ also show luminescence at room temperature when excited with ultraviolet (UV) to blue light. The maximum intensity of the emission band is found at 589 nm (fwhm = 145 nm)

Structural Redetermination and Photoluminescence Properties of the Niobium Oxyphosphate (NbO)₂P₄O₁₃

The structure of (NbO)₂P₄O₁₃ was solved and refined based on new single-crystal diffraction data revealing considerably more complexity than previously described. (NbO)₂P₄O₁₃ crystallizes in the triclinic space group <i>P</i>1̅ with <i>Z</i> = 6. The lattice parameters determined at room temperature are <i>a</i> = 1066.42(4) pm, <i>b</i> = 1083.09(4) pm, <i>c</i> = 1560.46(5) pm, α = 98.55(1)°, β = 95.57(1)°, γ = 102.92(1)°, and <i>V</i> = 1.7213(2) nm³. The superstructure contains 64 unique atoms including two disordered semioccupied oxygen positions. An unusual 180° bond angle between two [P₄O₁₃]^6– groups was refined to form half-occupied, split positions in agreement with previous reports. The IR and Raman spectra reflect the appearance of overlapping bands assignable to specific group vibrations as well as P–O–P linkages present in the [P₄O₁₃]^6– entities. Investigation of the powdered product concerning its photoluminescence properties revealed an excitability in the UV at 270 nm assigned to O2p–Nb4d charge transfer transitions. A resulting broad-band emission with the maximum in the visible region at 455 nm was determined

High-Pressure Synthesis and Characterization of Li₂Ca₃[N₂]₃An Uncommon Metallic Diazenide with [N₂]^2– Ions

Dinitrogen (N₂) ligation is a common and well-characterized structural motif in bioinorganic synthesis. In solid-state chemistry, on the other hand, homonuclear dinitrogen entities as structural building units proved existence only very recently. High-pressure/high-temperature (HP/HT) syntheses have afforded a number of binary diazenides and pernitrides with [N₂]^2– and [N₂]^4– ions, respectively. Here, we report on the HP/HT synthesis of the first ternary diazenide. Li₂Ca₃[N₂]₃ (space group <i>Pmma</i>, no. 51, <i>a</i> = 4.7747(1), <i>b</i> = 13.9792(4), <i>c</i> = 8.0718(4) Å, <i>Z</i> = 4, <i>wR</i>_p = 0.08109) was synthesized by controlled thermal decomposition of a stoichiometric mixture of lithium azide and calcium azide in a multianvil device under a pressure of 9 GPa at 1023 K. Powder X-ray diffraction analysis reveals strongly elongated N–N bond lengths of <i>d</i>_NN = 1.34(2)–1.35(3) Å exceeding those of previously known, binary diazenides. In fact, the refined N–N distances in Li₂Ca₃[N₂]₃ would rather suggest the presence of [N₂]^3·– radical ions. Also, characteristic features of the N–N stretching vibration occur at lower wavenumbers (1260–1020 cm^–1) than in the binary phases, and these assignments are supported by first-principles phonon calculations. Ultimately, the true character of the N₂ entity in Li₂Ca₃[N₂]₃ is probed by a variety of complementary techniques, including electron diffraction, electron spin resonance spectroscopy (ESR), magnetic and electric conductivity measurements, as well as density-functional theory calculations (DFT). Unequivocally, the title compound is shown to be metallic containing diazenide [N₂]^2– units according to the formula (Li⁺)₂(Ca²⁺)₃([N₂]^2–)₃·(e^–)₂

High-Pressure Synthesis and Characterization of Li₂Ca₃[N₂]₃An Uncommon Metallic Diazenide with [N₂]^2– Ions

Dinitrogen (N₂) ligation is a common and well-characterized structural motif in bioinorganic synthesis. In solid-state chemistry, on the other hand, homonuclear dinitrogen entities as structural building units proved existence only very recently. High-pressure/high-temperature (HP/HT) syntheses have afforded a number of binary diazenides and pernitrides with [N₂]^2– and [N₂]^4– ions, respectively. Here, we report on the HP/HT synthesis of the first ternary diazenide. Li₂Ca₃[N₂]₃ (space group <i>Pmma</i>, no. 51, <i>a</i> = 4.7747(1), <i>b</i> = 13.9792(4), <i>c</i> = 8.0718(4) Å, <i>Z</i> = 4, <i>wR</i>_p = 0.08109) was synthesized by controlled thermal decomposition of a stoichiometric mixture of lithium azide and calcium azide in a multianvil device under a pressure of 9 GPa at 1023 K. Powder X-ray diffraction analysis reveals strongly elongated N–N bond lengths of <i>d</i>_NN = 1.34(2)–1.35(3) Å exceeding those of previously known, binary diazenides. In fact, the refined N–N distances in Li₂Ca₃[N₂]₃ would rather suggest the presence of [N₂]^3·– radical ions. Also, characteristic features of the N–N stretching vibration occur at lower wavenumbers (1260–1020 cm^–1) than in the binary phases, and these assignments are supported by first-principles phonon calculations. Ultimately, the true character of the N₂ entity in Li₂Ca₃[N₂]₃ is probed by a variety of complementary techniques, including electron diffraction, electron spin resonance spectroscopy (ESR), magnetic and electric conductivity measurements, as well as density-functional theory calculations (DFT). Unequivocally, the title compound is shown to be metallic containing diazenide [N₂]^2– units according to the formula (Li⁺)₂(Ca²⁺)₃([N₂]^2–)₃·(e^–)₂