Synthesis and Luminescence Properties of Amber Emitting La7 Sr[Si10 N19 O3 ] : Eu2+ and Syntheses of the Substitutional Variants RE8-x AEx [Si10 N20-x O2+x ] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba; 0≤x≤2.

The oxonitridosilicate La7 Sr[Si10 N19 O3 ] : Eu2+ and its substitutional variants RE8-x AEx [Si10 N20-x O2+x ] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba and 0≤x≤2 were synthesized starting from REN, SrN/Ca3 N2 /Ba2 N, SiO2 , amorphous Si3 N4 and Eu2 O3 as doping agent at 1600 °C in a radiofrequency furnace. The crystal structure of La7 Sr[Si10 N19 O3 ] was solved and refined based on single-crystal X-ray diffraction data. La7 Sr[Si10 N19 O3 ] crystallizes in the orthorhombic space group Pmn21 (no. 31). The crystal structures of the isotypic compounds RE8-x AEx [Si10 N20-x O2+x ] were confirmed by Rietveld refinements based on powder X-ray diffraction data using the single-crystal data of La7 Sr[Si10 N19 O3 ] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN4 and SiN2 (N1/2-x/4 O1/2+x/4 )2 (0≤x≤2) tetrahedra. When excited with UV to blue light, La7 Sr[Si10 N19 O3 ] : Eu2+ shows amber luminescence with λem =612 nm and fwhm=84 nm/2194 cm-1 , which makes it interesting for application in amber phosphor-converted light emitting diodes.

Missing Member in the MII MIII Si4 N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si4 N7-2x Cx Ox ]:Eu2+ /Ce3+ (x≈0.3).

The nitridosilicate CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2 , Lu2 O3 , graphite and amorphous Si3 N4 at 1550 °C in a radiofrequency furnace. CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) crystallizes isotypically to many previously known MII MIII Si4 N7 compounds in the space group P63 mc, as was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of carbon into the crystal structure as a result of the carbothermal synthesis route was confirmed by 13 C and 29 Si MAS NMR spectroscopy. For the first time in the MII MIII Si4 N7 compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by carbon, resulting in an adjusted sum formula, CaLu[Si4 N7-2x Cx Ox ] (x≈0.3). When excited with UV-to-blue light, CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) shows an emission maximum in the blue spectral region (λem =484 nm; fwhm=4531 cm-1 ) upon doping with Ce3+ , whereas Eu2+ -doped CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) exhibits a yellow-green emission (λem =546 nm; fwhm=3999 cm-1 ).

Structure Elucidation of Complex Endotaxially Intergrown Lanthanum Barium Oxonitridosilicate Oxides by Combination of Microfocused Synchrotron Radiation and Transmission Electron Microscopy.

Single-crystalline domains in intergrown microcrystalline material of the new compounds Ba22.5+x La55-x [Si129 N240-x Ox ]O3 :Ce3+ and Ba25.5+x La77-x [Si170 N312-x O9+x ]O4 :Ce3+ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond-valence sums and by comparison with isostructural Sr28.5+x La75-x [Si170 N312-x O9+x ]O4 . Ce3+ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation.

Flux synthesis, crystal structures, and physical properties of new lanthanum vanadium oxyselenides.

The new lanthanum vanadium oxyselenides LaVSe2O, La5V3Se6O7, La5V3Se7O5, La7VSe5O7, and La13V7Se16O15 were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSe2O and La5V3Se6O7 adopt known structure types, whereas La5V3Se7O5, La7VSe5O7, and La13V7Se16O15 crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe6, VSe5O, and/or VSe4O2 octahedra, linked together by edge-sharing OLa4 and/or OLa3V tetrahedra forming fluorite-like ribbons. LaVSe2O, La5V3Se7O5, and La7VSe5O7 contain only V(iii) ions, whereby La5V3Se6O7 and La13V7Se16O15 contain mixtures of either V(iii)/V(iv) or V(iii)/V(v) cations. Magnetic measurements indicate Curie-Weiss paramagnetism and magnetic ordering of the vanadium moments at low temperatures. More precisely, we observe antiferromagnetism for La5V3Se6O7, metamagnetism for La5V3Se7O5, ferromagnetism for La7VSe5O7 and a complex magnetic structure for La13V7Se16O15.