RE4Ba2[Si12O2N16C3]:Eu2+ ( RE = Lu, Y): Green-Yellow Emitting Oxonitridocarbidosilicates with a Highly Condensed Network Structure Unraveled through Synchrotron Microdiffraction.

The oxonitridocarbidosilicates RE4Ba2[Si12O2N16C3]:Eu2+ ( RE = Lu, Y) were synthesized by carbothermal reactions starting from RE2O3, graphite, Ba2Si5N8, Si(NH)2, and Eu2O3. The crystal structure of Lu4Ba2[Si12O2N16C3]:Eu2+ was elucidated on a submicron-sized single crystal by a combination of transmission electron microscopy and microfocused synchrotron radiation. The compound crystallizes in trigonal space group P3 (no. 143) with a = 16.297(4) Å, c = 6.001(2) Å, and Z = 3 ( R1 = 0.0332, wR2 = 0.0834, GoF = 1.034). According to Rietveld refinements on powder X-ray diffraction data, Y4Ba2[Si12O2N16C3]:Eu2+ is isotypic with a = 16.41190(6) Å and c = 6.03909(3) Å. The crystal structures are built up of vertex-sharing SiC(O/N)3 tetrahedra forming star-shaped units [C[4](Si(O/N)3)4] with carbon atoms in fourfold bridging positions. Energy-dispersive X-ray spectroscopy and CHNS analysis correspond to the sum formula, lattice energy, and charge distribution calculations support the assignment of O/N/C atoms. When excited with UV to blue light, Eu2+-doped samples show green luminescence for RE = Lu (λem ≈ 538 nm, full width at half-maximum (fwhm) ≈ 3600 cm-1) and yellow emission in the case of RE = Y (λem ≈ 556 nm, fwhm ≈ 4085 cm-1).

Ammonothermal Synthesis, Optical Properties, and DFT Calculations of Mg2 PN3 and Zn2 PN3.

The phosphorus nitrides, Mg2 PN3 and Zn2 PN3 , are wide band gap semiconductor materials with potential for application in (opto)electronics or photovoltaics. For the first time, both compounds were synthesized ammonothermally in custom-built high-temperature, high-pressure autoclaves starting from P3 N5 and the corresponding metals (Mg or Zn). Alkali amides (NaNH2 , KNH2 ) were employed as ammonobasic mineralizers to increase solubility of the starting materials in supercritical ammonia through formation of reactive intermediates. Single crystals of Mg2 PN3 , with length up to 30 µm, were synthesized at 1070 K and 140 MPa. Zn2 PN3 already decomposes at these conditions and was obtained as submicron-sized crystallites at 800 K and 200 MPa. Both compounds crystallize in a wurtzite-type superstructure in orthorhombic space group Cmc21 , which was confirmed by powder X-ray diffraction. In addition, single-crystal X-ray diffraction measurements of Mg2 PN3 were carried out for the first time. To our knowledge, this is the first single-crystal X-ray study of ternary nitrides synthesized by the ammonothermal method. The band gaps of both nitrides were estimated to be 5.0 eV for Mg2 PN3 and 3.7 eV for Zn2 PN3 by diffuse reflectance spectroscopy. DFT calculations were carried out to verify the experimental values. Furthermore, a dissolution experiment was conducted to obtain insights into the crystallization behavior of Mg2 PN3 .

Ultra-Narrow-Band Blue-Emitting Oxoberyllates AELi2 [Be4 O6 ]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc-LEDs.

Highly efficient phosphor-converted light-emitting diodes (pc-LEDs) are popular in lighting and high-tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra-narrow band blue emitting oxoberyllates AELi2 [Be4 O6 ]:Eu2+ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi2 [(Al2 Si2 )N6 ]:Eu2+ . The oxoberyllates' extremely small Stokes shift and unprecedented ultra-narrow band blue emission with fwhm ≈25 nm (≈1200 cm-1 ) at λem =454-456 nm result from its rigid, highly condensed tetrahedra network. AELi2 [Be4 O6 ]:Eu2+ allows for using short-wavelength blue LEDs (λem <440 nm) for efficient excitation of the ultra-narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.

Oxonitridosilicate Oxides RE26Ba6[Si22O19N36]O16:Eu2+ (RE = Y, Tb) with a Unique Layered Structure and Orange-Red Luminescence for RE = Y.

The oxonitridosilicate oxides RE26Ba6[Si22O19N36]O16:Eu2+ (RE = Y, Tb) were synthesized by high-temperature reaction in a radiofrequency furnace starting from REF3, RE2O3 (RE = Y, Tb), BaH2, Si(NH)2, and EuF3. The structure elucidation is based on single-crystal X-ray data. The isotypic materials crystallize in the monoclinic space group Pm (no. 6) [Z = 3, a = 16.4285(8), b = 20.8423(9), c = 16.9257(8) Å, ß = 119.006(3)° for RE = Y and a = 16.5465(7), b = 20.9328(9), c = 17.0038(7) Å, ß = 119.103(2)° for RE = Tb]. The unique silicate layers are made up from Q1-, Q2-, and Q3-type Si(O/N)4- as well as Q4-type SiN4-tetrahedra, forming three slightly differing types of cages. The corresponding 3-fold superstructure as well as pronounced hexagonal pseudosymmetry complicated the structure elucidation. Rietveld refinement on powder X-ray diffraction data, energy-dispersive X-ray spectroscopy and infrared spectroscopy support the findings from single-crystal X-ray data. When excited with UV to blue light, Y26Ba6[Si22O19N36]O16:Eu2+ shows broad orange-red luminescence (λem = 628 nm, fwhm ≈ 125 nm/3130 cm-1). An optical band gap of 4.2 eV was determined for the doped compound by means of UV/vis spectroscopy.

Framework structures of interconnected layers in calcium iron arsenides.

The new calcium iron arsenide compounds Ca(n(n+1)/2)(Fe(1-x)M(x))(2+3n)M'(n(n-1)/2)As((n+1)(n+2)/2) (n = 1-3; M = Nb, Pd, Pt; M' = □, Pd, Pt) were synthesized and their crystal structures determined by single-crystal X-ray diffraction. The series demonstrates the structural flexibility of iron arsenide materials, which otherwise prefer layered structures, as is known from the family of iron-based superconductors. In the new compounds, iron arsenide tetrahedral layers are bridged by iron-centered pyramids, giving rise to so far unknown frameworks of interconnected FeAs layers. Channels within the structures are occupied with calcium and palladium or platinum, respectively. Common basic building blocks are identified that lead to a better understanding of the building principles of these structures and their relation to CaFe4As3.