Ni-vacancy defect in diamond detected by electron spin resonance

Trigonal $S=1$ NOL1/NIRIM5 center has been characterized by electron spin resonance (ESR) in nickel and boron doped diamond grown by the high-pressure high-temperature technique. Hyperfine interaction structure has been detected and attributed to six equivalent carbon sites and one Ni site. Analysis of the ESR parameters strongly suggests assignment of the NOL1/NIRIM5 center to interstitial ${\mathrm{Ni}}^{2+}$ ion ($3d^8$ configuration) situated in the center of a diamond divacancy.

Figure 1

Angular map (squares) of the ESR resonance fields for the NOL1/NIRIM5 center measured with a $Q$-band spectrometer at $20\mathrm{K}$ from a HPHT diamond rotated in the [1-10] plane. The lines were computer generated using the parameters listed in the text.

Figure 2

ESR spectrum recorded at $20\mathrm{K}$ around one of the NOL1/NIRIM5 lines using the modulation amplitude of $0.1\mathrm{mT}$ and microwave power $5\mu \mathrm{W}$. The simulation (line) suggests presence of hyperfine structure attributed to six equivalent carbon sites and one Ni site.

Figure 3

Angular map (squares) of the principal hyperfine splitting (six carbon sites) at the NOL1/NIRIM5 center measured for rotation in the [1-10] plane. The lines were computer generated using the isotropic hf constant $A=1.5\mathrm{mT}$.

Figure 4

Integrated intensity of the NOL1/NIRIM5 ESR signals and of the 1.22 and $1.4\mathrm{eV}$ optical absorption plotted as a function of energy of in situ illumination at $77\mathrm{K}$.