Diamond is a unique mineral widely used in diverse fields due to its remarkable properties. The development of synthesis technology made it possible to create diamond-based semiconductor devices. In addition, doped diamond can be used as single photon emitters in various luminescence applications. Different properties are the result of the presence of impurities or intrinsic defects in diamond. Thus, the investigation of the defect formation process is of particular interest. Although hydrogen, nitrogen, and boron have been known to form different point defects, the possibility for large impurity atoms to incorporate into the diamond crystal structure has been questioned for a long time. In the current paper, the paramagnetic nickel split-vacancy defect in diamond is described, and the further investigation of nickel-, cobalt-, titanium-, phosphorus-, silicon-, and germanium-related defects is discussed.

In this work, high pressure high temperature (HPHT) diamonds synthesized in the Mg-C system with germanium, silicon and boron additives were studied. In the photoluminescence spectra of the samples doped with Ge, an intense system 602 nm attributed to germanium-vacancy defects was detected. In the electron paramagnetic resonance (EPR) spectra of these samples, a new paramagnetic center with S ¼ 1 was detected along with substitutional nitrogen P1 and silicon-vacancy KUL1 (SiV 0 ) centers. The angular dependence investigation of the new spectrum allowed us to establish its spin Hamiltonian parameters: g || ¼ 2.0025, g ? ¼ 2.0027, D ¼ 80.3 mT, E ¼ 0. The center was determined to have the symmetry axis parallel to h111i. Hyperfine structure (HFS) of one 73 Ge atom (I ¼ 9/2) was observed for the new spectrum. The novel paramagnetic center was proposed to be the neutral germanium split-vacancy defect. EPR and luminescence studies of diamonds doped with Si and B revealed a new paramagnetic center that can be associated with the sharp luminescence system 720 nm. An analysis of the angular dependence of the EPR spectrum showed that it had electronic spin S ¼ 1/2 and anisotropic g-factor: g 1 ¼ 2.0033, g 2 ¼ 2.0004, and g 3 ¼ 2.0024. Based on the principal values and directions of the g-tensor the detected center was suggested to have the structure of silicon and boron atoms in the nearest carbon positions.

accompanied by the EPR center with g-factor of 2.00285. The 536 and 576 nm vibronic systems totally dominated the PL spectra of superdeep diamonds, while none of "normal" diamonds from the Mir pipe (Yakutia) with similar nitrogen characteristics showed the latter three PL centers.