Electron paramagnetic resonance and electron-nuclear double resonance study of trapped-hole centers in LiB3O5 crystals -: art. no. 094111
Electron paramagnetic resonance and electron-nuclear double resonance study of trapped-hole centers in LiB3O5 crystals -: art. no. 094111
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DOI：
10.1103/physrevb.68.094111
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发表时间：
2003-09-01
影响因子：
3.7
通讯作者：
Villeval, P
中科院分区：
文献类型：
--
作者：
Hong, W;Chirila, MM;Villeval, P
利用电子顺磁共振（EPR）和电子核双共振（ENDOR）表征了li3o5（通常称为LBO）单晶中两个不同的空穴中心。在77k下用x射线照射晶体会产生强烈的四线类空穴EPR信号，其结构是由与一个B-11核的超精细相互作用产生的。将晶体加热到大约130 K，破坏了第一个空穴中心，并允许观察到第二个强度较低的四线空穴EPR信号（也与一个B-11核相互作用）。第二个空穴中心在150 ~ 200k之间衰减。利用EPR和ENDOR的角相关数据确定了每个孔中心的g矩阵和B-11超精细和核四极矩阵。我们认为第一个中心（热稳定性较差）是一个自困洞。在这种缺陷中，空穴主要定位在三重键硼和四重键硼之间的氧离子上，并且由于邻近的四重键硼远离空穴的显著弛豫而发生自俘获。高斯98计算，使用（B3O7H4）(0)簇来表示缺陷和附近的晶格，支持这种自捕获机制。对于第二个空穴中心，也提出了类似的模型，只是在这种情况下，为了提供更高的热稳定性，增加了一个邻近的锂空位。这些困穴中心之所以引起人们的兴趣，是因为它们可能在室温下高功率脉冲紫外激光在LiB3O5晶体中产生的不需要的瞬态光吸收中起作用。
Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to characterize two distinct hole centers in single crystals of LiB3O5 (commonly referred to as LBO). Irradiating a crystal at 77 K with x rays produces an intense four-line holelike EPR signal, with the structure arising from the hyperfine interaction with one B-11 nucleus. Warming the crystal to approximately 130 K destroys the first hole center and allows a second less intense four-line holelike EPR signal to be observed (also interacting with one B-11 nucleus). The second hole center decays between 150 and 200 K. EPR and ENDOR angular dependence data were used to determine the g matrix and the B-11 hyperfine and nuclear quadrupole matrices for each hole center. We suggest that the first (less thermally stable) center is a self-trapped hole. In this defect, the hole is localized primarily on an oxygen ion between a threefold bonded boron and a fourfold bonded boron, and the self-trapping occurs because of a significant relaxation of the neighboring fourfold boron away from the hole. GAUSSIAN 98 calculations, using a (B3O7H4)(0) cluster to represent the defect and the nearby lattice, support this self-trapping mechanism. A similar model is suggested for the second hole center, except in this case a neighboring lithium vacancy is included to provide the increased thermal stability. These trapped-hole centers are of interest because of their possible role in the unwanted transient optical absorption produced in LiB3O5 crystals at room temperature by high-power pulsed ultraviolet lasers.