A New Paramagnetic Nitrogen Center in Natural Titanium-Containing Diamonds

A new type of nitrogen-related center in natural diamond labeled NU1 is identified as a 〈100〉 split interstitial configuration by means of electron paramagnetic resonance (EPR) and photoluminescence (PL) techniques. In PL this center is seen as an electron-vibration system with a zero-phonon line at 485 nm in the crystals containing S1/OK1 and 440.3 nm/N3 centers. NU1 EPR spectra are described by a spin-Hamiltonian with parameters: S = ½, I = 1 and A _xx (N) = 22.5 G, A _yy (N) = 19.5 G, A _zz (N) = 20.55 G, g _xx  = 2.0043, g _yy  = 2.0032, g _zz  = 2.0020. Directions of A _zz and g _zz coincide and correspond to 001]. The directions of A _xx and A _yy coincide with those of g _xx and g _yy and correspond to 110] and ?110], respectively. Analysis of the phonon structure of the NU1 center suggested that titanium can be the second atom together with nitrogen in the structure of a split interstitial.