A high-resolution magnetic circular dichroism ͑MCDA͒ 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 Ni i ϩ , 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 Ќ ϳ0) and excited (g ʈ ϳ0) states. A search for an optically detected magnetic resonance in the MCDA was unsuccessful, consistent with the forbidden magnetic resonance transition for an Sϭ1/2, g Ќ ϭ0 ground state. ͓S0163-1829͑99͒13231-4͔PRB 60 5423 MAGNETIC CIRCULAR DICHROISM OF THE 1.404-eV . . .
Two positive ODMR resonances are commonly observed on a luminescence band in GaN at 2.2 eV, one identified as a shallow donor, the other currently unidentified. We here report a study of their dependencies on a variety of experimental parameters, including microwave modulation frequency, microwave power, photoexcitation power and photoexcitation energy. ODMR simulations using two theoretical models are compared to experimental results which are consistent with spin-dependent recombination between the two defects, assuming the donor has a spin-lattice relaxation time shorter than the spin-dependent recombination lifetime. The photoexcitation energy dependence suggests that the spin-dependent recombination associated with the 2.2 eV band is not the same recombination that is responsible for the luminescence. This supports the two stage model put forth by Glaser et al. for the luminescence process.
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