Abstract The DFT based full-potential linear augmented plane-wave method has been employed to simulate computationally the Li2B4O7 scintillator with isolated Ag1+ impurity substituting for the Li1+ ion. With the objective to investigate the physics of the Ag1+ defect in pre- and post-irradiated compound, the unit cell of the Li2B4O7:Ag has been differently charged. It was found that additional electrons and holes were captured exactly by the Ag1+, confirming the experimental fact that this defect acts as an electron and a hole trapping center. It has been concluded that the Ag impurity can assume the Ag1+, Ag0, and Ag2+ charge states. The lattice position and the relaxed local structure around each of them have been determined and chemical bonding with neighboring atoms carefully analyzed. The Ag1+ defect is found to be dislocated from the Li site, while the Ag2+ is stabilized approximately at it, both being bonded only to neighboring oxygens. The Ag0 defect is dislocated from the Li site by approx. 1.0 A and bonded to the oxygens and one boron ion, a fact which classifies it as an interstitial defect. Electronic structure and absorption coefficient spectra of the compound containing each of the 3 charged defects have been calculated. A comparison of the obtained results with experimental data shows that the 4d10 → 4d95s1 transitions at the sole Ag1+ defect are responsible for the optical response of the pre-irradiated compound (peak centered on 6.0 eV). The Ag2+ and Ag0 defects contribute to the additional absorption bands which appear after the X-ray irradiation of the compound. The absorption peak centered on 1.9 eV is due to 4d → 4d electronic transitions at the Ag2+ centers, while the Ag0 center contributes to the creation of the broad absorption band spread between 2.5 and 5.5 eV via the 5s → 5p and the 4d → 5s transitions. The present study interprets the results of the recent experimental studies and substantiates, in the largest part, their conclusions. Additionally, it predicts a shift of the 1.9 eV absorption peak to lower energies as a response to the light polarized along the crystalline c-axis.

中文翻译：

---

Li2B4O7 闪烁体中置换 Ag 缺陷的结构、电子和光学表征

摘要 基于 DFT 的全电位线性增强平面波方法已被用于计算模拟 Li2​​B4O7 闪烁体与孤立的 Ag1+ 杂质替代 Li1+ 离子。为了研究辐照前和辐照后化合物中 Ag1+ 缺陷的物理特性，Li2B4O7:Ag 的晶胞带有不同的电荷。发现额外的电子和空穴被 Ag1+ 准确捕获，证实了该缺陷充当电子和空穴捕获中心的实验事实。已经得出结论，Ag 杂质可以呈现 Ag1+、Ag0 和 Ag2+ 电荷态。已经确定了它们每个周围的晶格位置和松弛的局部结构，并仔细分析了与相邻原子的化学键合。发现 Ag1+ 缺陷从 Li 位点错位，而 Ag2+ 大约稳定在它上面，两者都只与相邻的氧键合。Ag0 缺陷从 Li 位点错位约。1.0 A 并与氧和一个硼离子结合，这一事实将其归类为间隙缺陷。已经计算了包含 3 个带电缺陷中的每一个的化合物的电子结构和吸收系数光谱。将获得的结果与实验数据进行比较表明，唯一的 Ag1+ 缺陷处的 4d10 → 4d95s1 跃迁是预辐照化合物的光学响应（峰值集中在 6.0 eV）的原因。Ag2+ 和 Ag0 缺陷有助于在化合物的 X 射线照射后出现额外的吸收带。以 1.9 eV 为中心的吸收峰是由于 Ag2+ 中心的 4d → 4d 电子跃迁，而 Ag0 中心有助于通过 5s → 5p 和 4d → 5s 跃迁在 2.5 到 5.5 eV 之间产生宽吸收带扩展。本研究解释了最近的实验研究的结果，并在很大程度上证实了他们的结论。此外，它预测 1.9 eV 吸收峰向低能量移动，作为对沿晶体 c 轴偏振光的响应。