χ ¼ Jxx ¼ g2μB2=r3 is a component of the fine-structure tensor J that
describes the anisotropic interaction between the triplet and the
doublet spins (see Table 1). The g-values of the two centers are close
to that of the free-electron [23]. μB is the Bohr magneton and r the
relative distance between the two defects. The last term on
the right-hand side of Eq. (1) gives the Zeeman interaction between
the electron spins and the static magnetic field. ΔωL ¼ ðωL ωÞ
is the resonance detuning and ωL ¼ gμBB0 the Larmor frequency.
Terms that oscillate at 2ω have also been ignored (rotating-wave
approximation). The eigenvalues and eigenvectors of H0 are given
below: