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Sr(5)Al(5+x)Si(21-x)N(35-x)O(2+x) (x approximately 0) was obtained by high-temperature synthesis (1600 to 1750 degrees C). Upon doping with Eu(2+), the thermally very stable material shows an efficient broadband emission in the green spectral range (lambda(max) approximately 510 nm, FWHM = 69 nm) under UV to blue light excitation. The compound exhibits a complex intergrowth structure (space group Pmn2(1) (no. 31); a = 23.614, b = 7.487, c = 9.059 A; V = 1601.5(6) A(3); Z = 2, R1 = 0.067), which consists of highly condensed dreier ring layers alternating with sechser ring layers that include both vertex- and edge-sharing (Si,Al)(O,N)(4) tetrahedra. Both layer types exhibit pseudotranslational symmetry, which leads to a more or less pronounced disorder of the sechser ring layers. The Sr atoms are located in channel-like voids of the silicate framework with coordination number nine. The compound has been characterized by single-crystal and powder X-ray diffraction, as well as high-resolution electron microscopy and electron diffraction. The structure and chemical composition has been confirmed by (29)Si solid-state NMR spectroscopy, lattice energy calculations, and diverse elemental analyses.

Ba 2 AlSi 5 N 9 was synthesized starting from Si 3 N 4 , AlN, and Ba in a radio-frequency furnace at temperatures of about 1725 °C. The new nitridoalumosilicate crystallizes in the triclinic space group P1 (no. 1), a ) 9.860(1) Å, b ) 10.320(1) Å, c ) 10.346(1) Å, R ) 90.37(2)°, β ) 118.43(2)°; γ ) 103.69(2)°, Z ) 4, R1 ) 0.0314. All synthesized crystals were characteristically twinned by reticular pseudomerohedry with twin law (1 0 0, -0.5 -1 0, -1 0 -1). The crystal structure of Ba 2 AlSi 5 N 9 was determined from single-crystal X-ray diffraction data of a twinned crystal and confirmed by Rietveld refinement both on X-ray and on neutron powder diffraction data. Statistical distribution Si/Al is corroborated by lattice energy calculations (MAPLE). 29 Si and 27 Al solid-state NMR are in accordance with the crystallographic results. Ba 2 AlSi 5 N 9 represents a new type of network structure made up of TN 4 tetrahedra (T ) Si, Al). Highly condensed layers of dreier rings with nitrogen connecting three neighboring tetrahedral centers occur which are further crosslinked by dreier rings and vierer rings. The dreier rings consist of corner-sharing tetrahedra, whereas some of the vierer rings exhibit two pairs of edge-sharing tetrahedra. In the resulting voids of the network there are eight different Ba 2+ sites with coordination numbers between 6 and 10. Thermogravimetric investigations confirmed a thermal stability of Ba 2 AlSi 5 N 9 up to about 1515 °C (He atmosphere). Luminescence measurements on Ba 2 AlSi 5 N 9 :Eu 2+ (2 mol % Eu 2+ ) with an excitation wavelength of 450 nm revealed a broadband emission peaking at 584 nm (FWHM ) 100 nm) originating from dipole-allowed 4f 6 ( 7 F)5d 1 f 4f 7 ( 8 S 7/2 ) transitions.

The oxonitridoalumosilicates (so‐called sialons) MLn[Si4−xAlxOxN7−x] with M = Eu, Sr, Ba and Ln =Ho, Er, Tm, Yb were obtained by the reaction of the respective lanthanoid metal, the alkaline earth carbonates or europium carbonate, resp., AlN, “Si(NH)2” and MCl2 as a flux in a radiofrequency furnace at temperatures around 2100 °C. The compounds MLn[Si4−xAlxOxN7−x] are relevant for the investigation of substitutional effects on the materials properties due to their ability of tolerating a comparatively large phase width up to x ≈ 2.0(5). The crystal structures of the twelve compounds were refined from X‐ray single crystal data and X‐ray powder data and are found to be isotypic to the MYb[Si4N7] structure type. The compounds crystallize in space group P63mc (no. 186, hexagonal) and are made up of chains of so‐called starlike units [N[4](SiN3)4] or [N[4]((Si,Al)(O,N)3)4], respectively. These units are formed by four (Si,Al)(N/O)4 tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on the four‐fold bridging site and nitrogen and oxygen were distributed equally on both of the two‐fold bridging sites, resulting in charge neutrality of the compound. The Si and Al atoms were distributed equally on their two crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X‐ray methods. The chemical compositions of the compounds were derived from electron probe micro analyses (EPMA).