Missing Member in the M (II) M (III)Si(4)N(7) Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si(4)N(7–2x )C( x )O( x )]:Eu(2+)/Ce(3+) (x≈0.3)

The nitridosilicate CaLu[Si(4)N(7–2x )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 in a radiofrequency furnace. CaLu[Si(4)N(7–2x )C( x )O( x )] (x≈0.3) crystallizes isotypically to many previously known M (II) M (III)Si(4)N(7) compounds in the space group P6(3) 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 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 carbon, resulting in an adjusted sum formula, CaLu[Si(4)N(7–2x )C( x )O( x )] (x≈0.3). When excited with UV‐to‐blue light, CaLu[Si(4)N(7–2x )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+), whereas Eu(2+)‐doped CaLu[Si(4)N(7–2x )C( x )O( x )] (x≈0.3) exhibits a yellow‐green emission (λ (em)=546 nm; fwhm=3999 cm(−1)).