Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN₃

The first gallium‐containing nitridosilicate CaGaSiN 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 3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70–150 MPa). The impact of other mineralizers (e.g., LiN 3 , KN 3 , and CsN 3 ) on the product formation was investigated as well. The crystal structure of CaGaSiN 3 was analyzed by powder X‐ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29 Si MAS‐NMR, and first‐principle DFT calculations. CaGaSiN 3 crystallizes in the orthorhombic space group Cmc 2 1 (no. 36) with lattice parameters a =9.8855(11), b =5.6595(1), c =5.0810(1) Å, ( Z =4, R wp =0.0326), and is isostructural with CaAlSiN 3 (CASN). Eu 2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN 3 :Eu 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 3 :Eu 2+ , inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red‐emitting CASN type materials.