All spectra were recorded with an integration time of 300 s and 12 averaged accumulations (i.e., 1 hour of summed integration time). All samples were measured as manually compacted powders in a small stainless-steel mold. The Raman spectra were processed using R 3.5.1 by applying SNIP based baseline correction (100 iterations) and normalizing the spectra using Euclidean vector norm. FT Raman spectroscopy was performed on a Multispec FT-Raman spectrometer (Bruker Inc., Billerica, Massachusetts, United States of America). The excitation light at 1064 nm was provided by a Nd:YAG laser (Klastech DeniCAFC-LC-3/40, Dortmund, Germany). The spectra were recorded up to 4000 cm -1 with a spectral resolution of 4 cm - 1 . The laser power at the samples was set to 200 mW for R-CNx and 500 mW for Y-CNx. R-CNx-KS could not be measured using FT-Raman spectroscopy due to excessive photoluminescence.