State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.
School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China.
Molecules. 2021 Mar 25;26(7):1849. doi: 10.3390/molecules26071849.
We use density functional theory (DFT) to study the molecular structure and electronic band structure of SrSiN:Eu doped with trivalent lanthanides (Ln = Ce, Tb, Pr). Li was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr by Ln. The doping of Ln lanthanide atom causes the structure of SrSiN lattice to shrink due to the smaller atomic radius of Ln and Li compared to Sr. The doped structure's formation energy indicates that the formation energy of Li, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li doping site for double-doped lanthanide ions can be provided. In SrSiN:Eu, the doped Ce can occupy partly the site of Sr ([SrN]), while Eu accounts for Sr and Sr ([SrN]). When the Pr ion is selected as the dopant in SrSiN:Eu, Pr and Eu would replace Sr simultaneously. In this theoretical model, the replacement of Sr by Tb cannot exist reasonably. For the electronic structure, the energy level of SrSiN:Eu/Li doped with Ce and Pr appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of SrSiN. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of CeLi-SrSiN is from 2.42 to 2.85 eV. The energy range of 4f-CBM in PrLi-SrSiN is 2.75-2.99 eV and its peak is 2.90 eV; the addition of Ce in EuCeLi made the 4f energy level of Eu blue shift. The addition of Pr in EuPrLi makes part of the Eu 4f energy level blue shift. Eu 4f energy level in EuCeLi is not in the forbidden band, so Eu is not used as the emission center.
我们使用密度泛函理论（DFT）研究了 SrSiN：Eu 掺杂三价镧系元素（Ln = Ce、Tb、Pr）的分子结构和电子能带结构。Li 被用作 Sr 部分取代引起的电荷不平衡的电荷补偿剂。Ln 镧系原子的掺杂导致 SrSiN 晶格结构收缩，因为 Ln 和 Li 的原子半径比 Sr 小。掺杂结构的形成能表明，用于补偿电荷不平衡的 Li 的形成能在 Sr2 位掺杂时最低。因此，可以为双掺杂镧系离子提供合适的 Li 掺杂位。在 SrSiN：Eu 中，掺杂的 Ce 可以部分占据 Sr 位（[SrN]），而 Eu 占据 Sr 和 Sr 位（[SrN]）。当选择 Pr 离子作为 SrSiN：Eu 的掺杂剂时，Pr 和 Eu 会同时取代 Sr。在这个理论模型中，Tb 取代 Sr 是不合理的。对于电子结构，SrSiN：Eu/Li 掺杂 Ce 和 Pr 的能级出现在导带底部或禁带中，这降低了 SrSiN 的能带隙。我们使用 DFT+U 调整镧系离子 4f 能级。CeLi-SrSiN 的调整后 4f-CBM 从 2.42 到 2.85 eV。PrLi-SrSiN 的 4f-CBM 能量范围为 2.75-2.99 eV，峰值为 2.90 eV；EuCeLi 中 Ce 的加入使 Eu 的 4f 能级蓝移。EuPrLi 中 Pr 的加入使部分 Eu 4f 能级蓝移。EuCeLi 中的 Eu 4f 能级不在禁带中，因此 Eu 不作为发射中心。
