Missing Member in the MII MIII Si4 N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si4 N7-2x Cx Ox ]:Eu2+ /Ce3+ (x≈0.3).

Abstract

The nitridosilicate CaLu[Si4N7–2x C x O x ] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2, Lu2O3, graphite and amorphous Si3N4 at 1550 °C in a radiofrequency furnace. CaLu[Si4N7–2x C x O x ] (x≈0.3) crystallizes isotypically to many previously known M II M IIISi4N7 compounds in the space group P63 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 13C and 29Si MAS NMR spectroscopy. For the first time in the M II M IIISi4N7 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[Si4N7–2x C x O x ] (x≈0.3). When excited with UV‐to‐blue light, CaLu[Si4N7–2x 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 Ce3+, whereas Eu2+‐doped CaLu[Si4N7–2x C x O x ] (x≈0.3) exhibits a yellow‐green emission (λ em=546 nm; fwhm=3999 cm−1).