Missing Member in the MIIMIIISi4N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Revealing Substitution of N by C and O in CaLu[Si4N7-2xCxOx]:Eu2+/Ce3+ (x ≈ 0.3).

The nitridosilicate CaLu[Si 4 N 7-2 x C x O x ] ( x ≈ 0.3) was synthesized by carbothermal reduction and nitridation starting from CaH 2 , Lu 2 O 3 , graphite and amorphous Si 3 N 4 at 1550°C using a radiofrequency furnace. CaLu[Si 4 N 7-2 x C x O x ] ( x ≈ 0.3) crystallizes isotypic to many previously known M II M III Si 4 N 7 compounds in space group P 6 3 mc , which was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of C into the crystal structure as a result from the carbothermal synthesis route was confirmed via 13 C- and 29 Si-MAS-NMR spectroscopy. For the first time in the M II M III Si 4 N 7 compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by C, resulting in an adjusted sum formula, CaLu[Si 4 N 7-2 x C x O x ] ( x ≈ 0.3). When excited with UV to blue light, CaLu[Si 4 N 7-2 x C x O x ] ( x ≈ 0.3) shows an emission maximum in the blue spectral region ( λ em = 484 nm; fwhm = 4531 cm -1 ) upon doping with Ce 3+ , while Eu 2+ doped CaLu[Si 4 N 7-2 x C x O x ] ( x ≈ 0.3) exhibits a yellow-green emission ( λ em = 548 nm; fwhm = 4026 cm -1 ).