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).

The nitridosilicate CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2 , Lu2 O3 , graphite and amorphous Si3 N4 at 1550 °C in a radiofrequency furnace. CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) crystallizes isotypically to many previously known MII MIII Si4 N7 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 13 C and 29 Si MAS NMR spectroscopy. For the first time in the MII MIII Si4 N7 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[Si4 N7-2x Cx Ox ] (x≈0.3). When excited with UV-to-blue light, CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) shows an emission maximum in the blue spectral region (λem =484 nm; fwhm=4531 cm-1 ) upon doping with Ce3+ , whereas Eu2+ -doped CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) exhibits a yellow-green emission (λem =546 nm; fwhm=3999 cm-1 ).