Fig. 1. FESEM images of particles treated by microwave oxygen plasma for different times with inset showing histogram of particle size distribution of each sample.

Fig. 2. (a) PL spectra, variation of (b) position and FWHM values and (c) normalized intensity of Ge-V PL peak of samples with microwave oxygen plasma treatment time.

Fig. 3. (a) Raman spectra, (b) variation of position and FWHM of diamond peak in Raman spectra with microwave oxygen plasma treatment time, and (c) variation of diamond, graphite, and disordered carbon content of samples with microwave oxygen plasma treatment time.

Fig. 4. Schematic illustration of relationship between Ge-V PL and microstructure of diamond particles.