Synthesis and Structure of One-, Two-, and Three-Dimensional Alkaline Earth Metal Gallium Nitrides: Sr(3)Ga(2)N(4), Ca(3)Ga(2)N(4), and Sr(3)Ga(3)N(5)

Isomorphism of Sr[Li3AlO4] and Sr[Li3GaO4] - Syntheses, Crystal Structure, and Europium(II) Luminescence

While highly efficient red-emitting inorganic phosphors have been discovered in the substance class of alkaline earth oxo(nitrido)lithoaluminates, new narrow-band green- and yellow-emitting components are being sought to improve the performance of phosphor-converted light-emitting diodes (pc-LEDs). Various solid-state reactions were carried out under protective gas atmosphere in nickel crucibles and sealed tantalum ampules to synthesize Sr[Li3AlO4], Sr[Li3GaO4], and five substitutional derivates of Sr[Li3(Al1-x Ga x )O4] at moderate temperatures. The observation of a linear increase in the unit cell parameters as a function of the increasing gallium mole fraction x in Sr[Li3(Al1-x Ga x )O4] revealed Vegard behavior in the solid-solution series, which was derived from powder X-ray diffraction data. The isomorphic crystallization of the new oxolithogallate Sr[Li3GaO4] and the known oxolithoaluminate Sr[Li3AlO4] in an ordered variant of the U[Cr4C4] aristotype was verified on the basis of powder and single-crystal X-ray diffraction data. Photoluminescence spectroscopy was used to investigate the narrow-band emissions in the substitution series of Eu2+-activated Sr[Li3(Al1-x Ga x )O4] under blue-light excitation. The emission maximum was shifted to higher energies as the gallium mole fraction increased. Peak wavelengths were observed at λem = 572 nm (fwhm equals 47 nm, 1446 cm-1, 0.18 eV) for yellow-emitting Sr[Li3AlO4]:Eu2+ and at λem = 554 nm (fwhm equals 49 nm, 1589 cm-1, 0.20 eV) for green-emitting Sr[Li3GaO4]:Eu2+. Sr[Li3AlO4]:Eu2+ has excellent thermal quenching resistance with a photoluminescence emission intensity of >93% at T = 423 K relative to the room temperature value, making this inorganic phosphor a potential candidate for solid-state lighting applications.

Elastic, electronic, chemical bonding and thermodynamic properties of the ternary nitride Ca4TiN4: Ab initio predictions

In order to shed light on the unexplored properties of the ternary nitride Ca₄TiN₄, we report for the first time the results of an ab initio study of its structural, electronic, elastic, chemical bonding and thermodynamic properties. Calculated equilibrium structural parameters are in excellent concordance with available experimental data. Electronic properties were explored through the calculation of the energy band dispersions and density of states. It is found that Ca₄TiN₄ has an indirect band gap (Z-Γ) of 1.625 (1.701) eV using LDA (GGA). Nature of the chemical bonding was studied via Mulliken population analysis and charge density distribution map. It is found that the Ca-N bond is dominantly ionic, whereas the Ti-N one is dominantly covalent. Elastic properties of both single-crystal and polycrystalline phases of the title compound were explored in details using the stain-stress approach. Analysis of the calculated elastic moduli reveals that the title compound is mechanically stable, ductile and elastically anisotropic. Temperature and pressure dependencies of the unit-cell volume, bulk modulus, heat capacities, volume thermal expansion coefficient, Grüneisen parameter and Debye temperature were investigated based on the quasiharmonic Debye model.

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

One-step solid state reaction for the synthesis of ternary nitrides Co3Mo3N and Fe3Mo3N

Co₃Mo₃N and Fe₃Mo₃N have been synthesized by a one step solid-state reaction.

Metal Nitrides Grown from Ca/Li Flux: Ca6Te3N2 and New Nitridoferrate(I) Ca6(LixFe1-x)Te2N3

Two new tellurium-containing nitrides were grown from reactions in molten calcium and lithium. The compound Ca6Te3N2 crystallizes in space group R3̅c (a = 12.000(3)Å, c = 13.147(4)Å; Z = 6); its structure is an anti-type of rinneite (K3NaFeCl6) and 2H perovskite related oxides such as Sr3Co2O6. The compound Ca6(LixFe1-x)Te2N3 where x ≈ 0.48 forms in space group P42/m (a = 8.718(3)Å, c = 6.719(2)Å; Z = 2) with a new stuffed anti-type variant of the Tl3BiCl6 structure. Band structure calculations and easily observable red/green dichroic behavior indicate that Ca6Te3N2 is a highly anisotropic direct band gap semiconductor (Eg = 2.5 eV). Ca6(LixFe1-x)Te2N3 features isolated linear N-Fe-N units with iron in the rare Fe(1+) state. The magnetic behavior of the iron site was characterized by magnetic susceptibility measurements, which indicate a very high magnetic moment (5.16μB) likely due to a high degree of spin-orbit coupling. Inherent disorder at the Fe/Li mixed site frustrates long-range communication between magnetic centers.

Origin of thermal degradation of Sr(2-x)Si5N8:Eu(x) phosphors in air for light-emitting diodes

The orange-red emitting phosphors based on M(2)Si(5)N(8):Eu (M = Sr, Ba) are widely utilized in white light-emitting diodes (WLEDs) because of their improvement of the color rendering index (CRI), which is brilliant for warm white light emission. Nitride-based phosphors are adopted in high-performance applications because of their excellent thermal and chemical stabilities. A series of nitridosilicate phosphor compounds, M(2-x)Si(5)N(8):Eu(x) (M = Sr, Ba), were prepared by solid-state reaction. The thermal degradation in air was only observed in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10, but it did not appear in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.02 and Ba analogue with x = 0.10. This is an unprecedented investigation to study this phenomenon in the stable nitrides. The crystal structural variation upon heating treatment of these compounds was carried out using the in situ XRD measurements. The valence of Eu ions in these compounds was determined by electron spectroscopy for chemical analysis (ESCA) and X-ray absorption near-edge structure (XANES) spectroscopy. The morphology of these materials was examined by transmission electron microscopy (TEM). Combining all results, it is concluded that the origin of the thermal degradation in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10 is due to the formation of an amorphous layer on the surface of the nitride phosphor grain during oxidative heating treatment, which results in the oxidation of Eu ions from divalent to trivalent. This study provides a new perspective for the impact of the degradation problem as a consequence of heating processes in luminescent materials.

Two New Structurally Related Strontium Gallium Nitrides: Sr4GaN3O and Sr4GaN3(CN2)

The strontium gallium oxynitride Sr(4)GaN(3)O and nitride-carbodiimide Sr(4)GaN(3)(CN(2)) are reported, synthesized as single crystals from molten sodium at 900 degrees C. Red Sr(4)GaN(3)O crystallizes in space group Pbca (No. 61) with a = 7.4002(1) Angstroms, b = 24.3378(5) Angstroms, c = 7.4038(1) Angstroms, and Z = 8, as determined from single-crystal X-ray diffraction measurements at 150 K. The structure may be viewed as consisting of slabs [Sr(4)GaN(3)](2+) containing double layers of isolated [GaN(3)](6-) triangular anions arranged in a "herringbone" fashion, and these slabs are separated by O(2-) anions. Brown Sr(4)GaN(3)(CN(2)) has a closely related structure in which the oxide anions in the Sr(4)GaN(3)O structure are replaced by almost linear carbodiimide [CN(2)](2-) anions [Sr(4)GaN(3)(CN(2)): space group P2(1)/c (No. 14), a = 13.4778(2) Angstroms, b = 7.4140(1) Angstroms, c = 7.4440(1) Angstroms, beta = 98.233(1) degrees, and Z = 4].

The indium subnitrides Ae6In4(InxLiy)N(3-z)(Ae = Sr and Ba)

The indium nitrides Sr6In4(In(0.32)Li(0.92))N(2.49) and Ba6In(4.78)N(2.72) have been synthesized from an excess of molten sodium. They crystallize in a stuffed variant of the eta-carbide structure type in the cubic space group Fdm with Z = 8. The lattice parameters are a = 14.3752(4) and 15.216(1) A, with cell volumes 2970.6(2) and 3523.3(6) A3, respectively. In both compounds there are vacancies on some of the indium and nitrogen sites and, in the case of Sr6In4(In(0.32)Li(0.92))N(2.49), mixed lithium-indium occupancy of one metal site. It is demonstrated that the partial and mixed occupancies act to carefully tune to electron count to almost fulfill the bonding requirements of the stellar quadrangular subnets of both compounds. Four probe resistivity measurements performed upon a pellet of Sr6In4(In(0.32)Li(0.92))N(2.49) show it to have a room-temperature resistivity of 6.3 mOmega.cm with a weak temperature dependence.

Synthesis and Structure of Alkaline Earth Silicon Nitrides: BaSiN2, SrSiN2, and CaSiN2

The alkaline earth silicon nitrides AESiN(2) (AE = Ca, Sr, Ba) are reported, synthesized as clear, colorless, single crystals from molten sodium at 900-1100 degrees C or, in the cases of BaSiN(2) and SrSiN(2), as white powders by reacting powdered intermetallics AESi with flowing anhydrous ammonia at 550-1000 degrees C. Structures were determined from single-crystal X-ray diffraction measurements at 150 K: BaSiN(2) crystallizes in space group Cmca (No. 64) with a = 5.6046(1) A, b = 11.3605(3) A, c = 7.5851(2) A, and Z = 8. The structure consists of pairs of SiN(4) tetrahedra edge-linked to form bow-tie-shaped Si(2)N(6) dimers which share vertexes to form layers and has no analogue in oxide chemistry. SrSiN(2) has a distorted form of this structure (SrSiN(2): space group P2(1)/c (No. 14), a = 5.9750(5) A, b = 7.2826(7) A, c = 5.4969(4) A, beta = 113.496(4) degrees, Z = 4). The structure of CaSiN(2) contains only vertex-sharing SiN(4) tetrahedra, linked to form a three-dimensional stuffed-cristobalite type framework isostructural with KGaO(2) (CaSiN(2): space group Pbca (No. 61), a = 5.1229(3) A, b = 10.2074(6) A, c = 14.8233(9) A, Z = 16).

Synthesis and structure of Sr3GaN3 and Sr6GaN5: strontium gallium nitrides with isolated planar [GaN3]6- anions

Two new strontium gallium nitrides were obtained as single crystals by reaction in molten Na. Black Sr(3)GaN(3) is isostructural with its transition metal analogues, Sr(3)MnN(3), Ba(3)MnN(3), Sr(3)CrN(3), Ba(3)CrN(3), and Ba(3)FeN(3), and is the first example of a 313-ternary nitride containing only main group metals. It crystallizes in space group P6(3)/m (No. 176) with a = 7.584(2) A, c = 5.410(3) A, and Z = 2. Black Sr(6)GaN(5) is isostructural with Ca(6)GaN(5) and also with its transition metal analogues, Ca(6)MnN(5) and Ca(6)FeN(5). It crystallizes in space group P6(3)/mcm (No. 193) with a = 6.6667(6) A, c = 12.9999(17) A, and Z = 2. Both Ga compounds contain isolated planar [GaN(3)](6)(-) nitridometallate anions of D(3)(h)() symmetry.

Crystal structures of two polymorphs of Ca3[Al2N4]

Green transparent single crystals of alpha-Ca3[Al2N4] (monoclinic, P2(1)/c, No. 14, a = 957.2(3) pm, b = 580.2(3) pm, c = 956.3(5) pm, beta = 111.62(3) degrees; Z = 4) were obtained from reactions of mixtures of the representative metals with nitrogen above temperatures of 1000 degrees C. beta-Ca3[Al2N4] (monoclinic, C2/c, No. 15, a = 1060.6(2) pm, b = 826.0(2) pm, c = 551.7(1) pm, beta = 92.1(1) degrees; Z = 4) was formed as a byproduct of a reaction of calcium with alumina under nitrogen at T = 930 degrees C in form of colorless crystals. The crystal structures of the two polymorphs contain edge- and corner-sharing AlN4 tetrahedra, leading to different layered anionic partial structures: infinity 2[AlN2/2N2/3)2(AlNN2/2N1/3)6/3(12-)] in the alpha-phase and infinity 2[Al2N2N4/2(6-)] in the beta-polymorph.

New calcium germanium nitrides: Ca2GeN2, Ca4GeN4, and Ca5Ge2N6

We report three new calcium germanium nitrides synthesized as crystals from the elements in sealed niobium tubes at 760 degrees C using liquid sodium as a growth medium. Black Ca2GeN2 is isostructural with the previously reported strontium analogue. It is tetragonal P4(2)/mbc (no. 135) with a = 11.2004(8) A, c = 5.0482(6) A, and Z = 8. It contains GeN2(4-) units which have 18 valence electrons, and consequently are bent, like the isoelectronic molecule SO2. In contrast, clear, orange Ca4GeN4 with fully oxidized germanium contains isolated GeN4(8-) tetrahedra and is monoclinic P2(1)/c (no. 14) with a = 9.2823(8) A, b = 6.0429(5) A, c = 11.1612(9) A, beta = 116.498(6) degrees, and Z = 4. Clear, colorless Ca5Ge2N6, also with fully oxidized germanium, contains infinite chains, 1 infinity[GeN2N2/2(5-)], of corner-sharing tetrahedra similar to those found in pyroxenes. However, the precise structure of this latter phase has not yet been determined because of twinning problems.