Excited states of the vacancy in diamond

The Coulson-Kearsley molecular model has been applied to various forms of the vacancy in diamond with considerable success from the point of view of group theory. Electron-electron interaction and configuration mixing are two important features of the molecular model which is reexamined with the intention of explaining why the model has been so successful to date. Parameters representing both one-electron and electron-electron interactions are deduced within an empirical framework of the molecular approach and are shown to consistently explain several properties of both GR1 (neutral vacancy) and ND1 (negative vacancy) optical features. Conclusions are reached concerning the position of neutral and negative vacancy energy levels relative to the valence-band edges. It is shown that optical properties of the neutral vacancy and the negative vacancy are strongly affected by charge-transfer excitations such that optical transitions are more probable at V^- than at V⁰. The optical transition proababilities for ND1 relate strongly to GR2--8 such that the probability of bound excitonic transitions at V⁰ can become considerably enhanced. The molecular multiplet structure of V⁰ is extended to include the effects of electron-electron correlation with bound excitonic states and this is shown to explain several properties of GR2--8.