27Al NMR relaxation studies of an emerald single crystal

The nuclear magnetic resonance of the 27Al nucleus in an emerald (Be3Al2Si6O18:Cr3+) single crystal grown by the flux method has been investigated in the temperature range of 120–420 K. The nuclear quadrupole coupling constant (e2qQ/h) and asymmetry parameter (η), 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–lattice relaxation mechanisms were investigated in the whole temperature range, and the result revealed that the Raman process was dominant above 200 K, and the contribution from the paramagnetic impurity became much larger than the quadrupole relaxation below 200 K. This is confirmed by analyzing the activation energy of the paramagnetic Cr3+ impurity.