Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN sub(3)

• Published in: Chemistry : a European journal 2017-02, Vol.23 (11), p.2583-2590
• Main Authors: Haeusler, Jonas, Neudert, Lukas, Mallmann, Mathias, Niklaus, Robin, Kimmel, Anna-Carina L, Alt, Nicolas SA, Schluecker, Eberhard, Oeckler, Oliver, Schnick, Wolfgang
• Format: Article
• Language: English
• Subjects: Autoclaves; Crystal structure; Gallium; Inclusions; Luminescence; Nitrides; Synthesis; Tuning
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201605344

The first gallium-containing nitridosilicate CaGaSiN sub(3) was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN sub(3) as a mineralizer. At 770K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070K (70-150MPa). The impact of other mineralizers (e.g., LiN sub(3), KN sub(3), and CsN sub(3)) on the product formation was investigated as well. The crystal structure of CaGaSiN sub(3) was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, super(29)SiMAS-NMR, and first-principle DFT calculations. CaGaSiN sub(3) crystallizes in the orthorhombic space group Cmc2 sub(1) (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1)Aa, (Z=4, R sub(wp)=0.0326), and is isostructural with CaAlSiN sub(3) (CASN). Eu super(2+) doped samples exhibit red luminescence with an emission maximum of 620nm and FWHM of 90nm. Thus, CaGaSiN sub(3):Eu super(2+) also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN sub(3):Eu super(2+), inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials. High-pressure ammonolysis: The novel nitridogallosilicate CaGaSiN sub(3):Eu super(2+) was synthesized as a new variant of CASN-type materials by the ammonothermal method and features promising luminescence properties for the application in phosphor-converted LEDs.