Synthesis of diamond microcrystals with a unique diversity of NiN<sub><em>x</em></sub> color centers by spontaneous crystallization using a nickel catalyst and europium oxide

Synthetic diamonds grown at high pressure and high temperature by spontaneous crystallization using a nickel catalyst and europium oxide additive exhibit emission spectra caused by a large morphological diversity of luminescence centers. It was found that most emission lines are associated with complex impurity centers of the NiN<sub><em>x</em></sub> composition (consisting of several nickel and nitrogen atoms) in a covalent diamond lattice. It was shown that the addition of europium oxide promotes an increase in the concentration of nickel Ni<sub>s</sub><sup>−</sup> centers in the crystals.