Optical Investigation of ¹²C Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition

Single‐crystal (SCD) and polycrystalline diamonds (PCD) are grown using microwave plasma chemical vapor deposition with high‐purity 12 C isotopically enriched methane (99.9% in chemical composition, 99.999% in isotopic enrichment). The PL spectra are measured under room and cryogenic temperatures with various laser excitation sources. An intensive signal near 699 nm, with the PL decay time ≈17 ns (excitation 532 nm, T = 77 K), is observed in the series of 12 C PCD films grown on Si substrates, while it is not detected in the epitaxial 12 C SCD grown on SCD substrate. Detailed PL characterization is conducted, and the results reveal that the peak is sensitive to the excitation source, but no experimental correlations with the expected phonon sideband in diamond are detected. The full width at half‐maximum (FWHM) of the peak at room temperature is ≈3 nm, while at cryogenic temperatures it splits into a number of shifted yet narrower peaks with FWHM of ≈0.05 nm. The emitter has a high degree of linear polarization, and its measured PL characteristics suggest that the emitters are unlikely to be associated with diamond, and it is speculated that it is related to the specific phase or defect in the sp 2 grain boundaries.