Missing Member in the MIIMIIISi4N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si4N7-2xCxOx]:Eu2+/Ce3+ (x≈0.3)

The nitridosilicate CaLu[Si4N7-2xCxOx] (x approximate to 0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2, Lu2O3, graphite and amorphous Si3N4 at 1550 degrees C in a radiofrequency furnace. CaLu[Si4N7-2xCxOx] (x approximate to 0.3) crystallizes isotypically to many previously known (MMSi4N7)-M-II-Si-III 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 C-13 and Si-29 MAS NMR spectroscopy. For the first time in the (MMSi4N7)-M-II-Si-III 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[Si4N7-2xCxOx] (x approximate to 0.3). When excited with UV-to-blue light, CaLu[Si4N7-2xCxOx] (x approximate to 0.3) shows an emission maximum in the blue spectral region (lambda(em)=484 nm; fwhm=4531 cm(-1)) upon doping with Ce3+, whereas Eu2+-doped CaLu[Si4N7-2xCxOx] (x approximate to 0.3) exhibits a yellow-green emission (lambda(em)=546 nm; fwhm=3999 cm(-1)).