Terblanche C J, Reynhardt E C, van Wyk J A
Department of Physics, University of South Africa, Pretoria.
Solid State Nucl Magn Reson. 2001 Aug-Sep;20(1-2):1-22. doi: 10.1006/snmr.2001.0026.
13C spin-lattice relaxation times in the laboratory frame, ranging from 1.4 to 36 h, have been measured on a suite of five natural type Ia and Ib diamonds at 4.7 T and 300 K. Each of the diamonds contains two types of fixed paramagnetic centers with overlapping inhomogeneous electron paramagnetic resonance (EPR) lines. EPR techniques have been employed to identify these defects and to determine their concentrations and relaxation times at X-band. Spin-lattice relaxation behavior of 13C in diamonds containing paramagnetic P1, P2, N2. and N3 centers are discussed. Depending on the paramagnetic impurity types and concentrations present in each diamond, three different nuclear spin-lattice relaxation (SLR) paths exist, namely that due to electron SLR mechanisms and two types of three-spin processes (TSPs). The one three-spin process (TSP1) involves a simultaneous transition of two electron spins belonging to the same hyperfine EPR line and a flip of a 13C spin, while the other process (TSP2) involves two electron spins belonging to different hyperfine EPR lines and a 13C spin. It is shown that the thermal contact between the 13C nuclear Zeeman and electron dipole-dipole interaction reservoirs is field dependent, thus forming a bottleneck in the 13C relaxation path due to TSP1 at high magnetic fields.
在4.7 T和300 K条件下，对一组五颗天然Ia型和Ib型钻石测量了实验室坐标系中的13C自旋晶格弛豫时间，范围为1.4至36小时。每颗钻石都包含两种类型的固定顺磁中心，其非均匀电子顺磁共振（EPR）线相互重叠。已采用EPR技术识别这些缺陷，并在X波段确定它们的浓度和弛豫时间。讨论了含有顺磁P1、P2、N2和N3中心的钻石中13C的自旋晶格弛豫行为。根据每颗钻石中存在的顺磁杂质类型和浓度，存在三种不同的核自旋晶格弛豫（SLR）路径，即由于电子SLR机制和两种类型的三自旋过程（TSP）。一种三自旋过程（TSP1）涉及属于同一超精细EPR线的两个电子自旋的同时跃迁和一个13C自旋的翻转，而另一种过程（TSP2）涉及属于不同超精细EPR线的两个电子自旋和一个13C自旋。结果表明，13C核塞曼与电子偶极-偶极相互作用库之间的热接触与磁场有关，因此在高磁场下由于TSP1在13C弛豫路径中形成了一个瓶颈。
