Temperature dependence of the electric field gradient parameters at ¹⁹F lattice sites in semiconducting and insulating diamonds

The electric field gradient parameters in insulating and semiconducting diamond, types IIa and IIb respectively, were measured as a function of temperature at residence sites of recoil implanted ¹⁹F by using the time-dependent perturbed angular distribution nuclear solid state technique. An improved experimental arrangement enables three distinct residence sites to be resolved, where only two had been resolved before. These correspond to quadrupole coupling constants of 62(1), 56(2) and 31(3) MHz. A strong temperature dependence in the fractional population of the second site was observed and is different for each of the two types of diamond. These measurements provide additional evidence for the explanation of this temperature dependence, i.e. a charge transfer from the lattice to the ¹⁹F occurs, which leads to the formation of the negative fluorine ion.