Electron paramagnetic resonance studies of silicon-related defects in diamond

We report the results of multifrequency electron paramagnetic resonance studies at temperatures between 8 and 300 K on diamonds synthesized by chemical vapor deposition and intentionally silicon doped with isotopes in natural abundance or isotopically enriched. The ²⁹Si hyperfine structure has provided definitive evidence for the involvement of silicon in two electron paramagnetic resonance centers in diamond that were previously suspected to involve silicon: KUL1 and KUL3. We present data that unambiguously identify KUL1 as an $S=1$ neutral silicon split-vacancy (D3d symmetry) defect (V-Si-V)⁰, while KUL3 is shown to be (V-Si-V)⁰ decorated with a hydrogen atom, (V-Si-V:H)⁰.