THE USE OF ENDOR TO IDENTIFY THE ATOMIC-STRUCTURE OF DEFECTS IN DIAMOND

Although nearly 100 paramagnetic defects have been catalogued in diamo nd by spin Hamiltonian parameters measured by electron paramagnetic re sonance (EPR), very few of these have been unambiguously associated wi th an atomic model. It has been necessary to use electron nuclear doub le resonance (ENDOR) to obtain enough information to make proper assig nment of such models. The reason for the limitation of EPR, and the wa y in which ENDOR overcomes these limitations are discussed. The interp retation of hyperfine structure in terms of unpaired electrons in mole cular orbitals, and of quadrupole interactions in terms of all electro ns, paired and unpaired, as a source of information about molecular st ructure in diamond, is evaluated by reference to some well documented examples. The measurements so far made by ENDOR on defects in diamond are reviewed, and the salient contribution for the assignment of a mod el for each defect is explained. The details revealed by ENDOR conside rably increase knowledge about defects, particularly those involving s ubstitutional nitrogen atoms. This in turn helps in understanding the complex electron and atom, migration processes which go on under appro priate conditions of temperature and pressure, or optical excitation. The possibilities are discussed for using ENDOR to increase the number of well characterized centres.