Abstract Quantum-mechanical effects of incorporation of the Cu ions at the Li sites in Li2B4O7 crystal matrix are investigated by means of first-principles calculations on density-functional-theory level. The isolated Cu defect is considered in various charge states with objective to simulate situations of the capture of an electron or a hole. In all cases the defective crystal is computationally relaxed, Cu-O chemical bonds carefully analyzed and local structure around the defects precisely determined. It is found that the defect vastly perturbs its O neighborhood and the Cu itself exhibits significant off-site dislocation from initial Li position in its Cu1+ and Cu0 charge states, while the Cu2+ stabilizes approximately at the Li site. Resulting defect formation energies demonstrate that the Cu1+ and Cu0 centers are the most stable ones. Electronic structure calculations reveal that the Cu introduces its d- and s-states within the gap and their energies and occupation depend strongly on the charge state of the defect. Experimental optical absorption spectra are well reproduced by the sole Cu1+ defect spectra, leading to the conclusion that in the as-grown material just Cu1+ centers are formed, with possible presence of small concentration of the Cu2+ centers. In the case of irradiated material, present study predicts formation of the interstitial Cu0 defects, whose presence should significantly change the optical absorption and emission of the material.

中文翻译：

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Li 2 B 4 O 7 闪烁体中Cu置换缺陷的结构、电子、能量和光学性质的第一性原理研究

摘要 通过密度泛函理论水平的第一性原理计算，研究了在 Li2B4O7 晶体基质中的 Li 位点掺入 Cu 离子的量子力学效应。孤立的铜缺陷在各种电荷状态下被考虑，目的是模拟电子或空穴的捕获情况。在所有情况下，有缺陷的晶体在计算上都是松弛的，仔细分析了 Cu-O 化学键，并精确确定了缺陷周围的局部结构。发现该缺陷极大地扰乱了其 O 邻域，并且 Cu 本身在其 Cu1+ 和 Cu0 电荷态的初始 Li 位置表现出显着的异位位错，而 Cu2+ 大约稳定在 Li 位点。产生的缺陷形成能表明 Cu1+ 和 Cu0 中心是最稳定的。电子结构计算表明，Cu 在间隙内引入了其 d 态和 s 态，它们的能量和占据在很大程度上取决于缺陷的电荷状态。实验光吸收光谱由唯一的 Cu1+ 缺陷光谱很好地再现，得出的结论是在生长的材料中仅形成 Cu1+ 中心，可能存在小浓度的 Cu2+ 中心。在辐照材料的情况下，本研究预测会形成间隙 CuO 缺陷，其存在应显着改变材料的光吸收和发射。实验光吸收光谱由唯一的 Cu1+ 缺陷光谱很好地再现，得出的结论是在生长的材料中仅形成 Cu1+ 中心，可能存在小浓度的 Cu2+ 中心。在辐照材料的情况下，本研究预测会形成间隙 CuO 缺陷，其存在应显着改变材料的光吸收和发射。实验光吸收光谱由唯一的 Cu1+ 缺陷光谱很好地再现，得出的结论是在生长的材料中仅形成 Cu1+ 中心，可能存在小浓度的 Cu2+ 中心。在辐照材料的情况下，本研究预测会形成间隙 CuO 缺陷，其存在应显着改变材料的光吸收和发射。