THE R2 EPR CENTER AND 1.685 EV ABSORPTION-LINE IN DIAMOND

The R2 EPR centre and 1.685 eV zero-phonon line seen in the optical ab sorption spectrum of diamond, have been shown to correlate in intensit y and are believed to be associated with the same defect. We propose t hat the defect responsible is a highly strained vacancy. the origin of strain possibly being a carbon interstitial. Existing stress paramete rs for the neutral vacancy are shown to predict an energy level struct ure in good agreement with those proposed for the R2 EPR and 1.685 eV centres. Furthermore, the model identifies the T-3(1) level of the unp erturbed neutral vacancy (predicted theoretically but not observed pre viously) as being located up to 200 meV above the (1)E ground state.