Magnetic circular dichroism of the 1.404-eV interstitial nickel absorption transition in high-pressure synthetic diamond

A high-resolution magnetic circular dichroism (MCDA) study of the sharp 1.404-eV zero-phonon absorption line associated with interstitial nickel in high-pressure synthetic diamond is reported. A model is presented attributing the absorption to internal transitions within the ${3d}^9$ configuration of ${\mathrm{Ni}}_i^{+},$ as perturbed by the cubic field at the diamond interstitial site, plus a smaller trigonal crystal field. The model provides a consistent explanation of the signs of the circular absorption coefficients of all the observed transitions plus the unusual features of the g values observed for the ground ${(g}_{\perp }\sim 0)$ and excited ${(g}_{\Vert }\sim 0)$ states. A search for an optically detected magnetic resonance in the MCDA was unsuccessful, consistent with the forbidden magnetic resonance transition for an $S=1/2,$ $g_{\perp }=0\mathrm{}$ ground state.