New theoretical model for the diamond 1s core exciton

The binding energy of the diamond 1s core exciton has a measured value of 0.2 eV, in marked contrast to the 1.7-eV binding energy of the physically similar nitrogen donor in diamond. Using the local-density approximation to study the core exciton, we find the shallow exciton binding energy is explained by dipole selection rules which prohibit occupation of a deep exciton gap state in single-photon excitation. This deep state has not yet been observed experimentally, and the calculation predicts a binding energy in the range of 0.8, 1.7 eV.