DYNAMIC NUCLEAR-POLARIZATION OF DIAMOND - II - NUCLEAR ORIENTATION VIA ELECTRON SPIN-LOCKING

The polarization of C-13 nuclei by means of nuclear orientation via el ectron spin-locking (Hartmann-Hahn cross-polarization between paramagn etic electrons and C-13 nuclei) in a suite of natural diamonds has bee n investigated at 2.4 GHz and 9.6 GHz. The C-13 polarization rate has been found to be independent of the microwave frequency, in agreement with theory. It is shown that since T-1 rho(e) much less than T-1(e) f or diamond, the effective polarization rate of C-13 nuclei is relative ly low. At low paramagnetic impurities (C-e < 5 ppm) C-13 nuclei in di amond are polarized faster by employing continuous wave microwave radi ation to drive the forbidden transitions of the C-13-electron spin sys tem, the so-called solid effect. (C) 1998 American Institute of Physic s. [S0021-9606(98)02633-6].