Observation of the Ge-vacancy color center in microcrystalline diamond films

In germanium-doped thin polycrystalline diamond films grown in microwave plasma on Ge substrates, strong photoluminescence in the orange spectral region with a zero-phonon line (ZPL) at a wavelength of 602 nm is detected. The ZPL width is 4–5 nm at room temperature and 1.2 nm at T = 5K. It is assumed that the new optically active defect is a germanium–vacancy (Ge–V) complex similar to the known Si–V color center in diamond.