Al-27 NMR relaxation studies of an emerald single crystal

The nuclear magnetic resonance of the Al-27 nucleus in an emerald (Be3Al2Si 6O18:Cr3+) Single crystal grown by the flux method has been investigated in the temperature range of 120-420 K. The nuclear quadrupole coupling consta nt (e(2)qQ/h) and asymmetry parameter (eta), were determined to be 3.123 +/ - 0.005 MHz and 0.0076 +/- 0.0064, respectively, at room temperature. There was no appreciable temperature dependence of these parameters. The spin-la ttice relaxation mechanisms were investigated in the whole temperature rang e, and the result revealed that the Raman process was dominant above 200 K, and the contribution from the paramagnetic impurity became much larger tha n the quadrupole relaxation below 200 K. This is confirmed by analyzing the activation energy of the paramagnetic Cr3+ impurity. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.