Abstract In this paper, the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional is employed to explore the structural, electronic, and optical properties of M2Si5N8:Eu2+ phosphors (M = Mg, Ca, Sr, Ba) on the ground–state and excited–state levels. From the detailed study of electronic structures of pure M2Si5N8, the top of the valence band is predominantly of N p character and the calculated band gaps are consistent with the reported experimental values. By Eu doping, the occupied 4f band is located directly in the band gap and results in the optical transition of the 4f–5d character. In order to confirm the location of the Eu 5d band below the conduction band, the excited–state calculation was executed. Using the position of the lowest excited–state 5d band below the conduction band, the calculated 4f–5d energy gaps agrees well with the experimental data. The excited–state calculation confirms that the Eu2+ d–f emission will be predominant in these phosphors. Furthermore, in order to understand and explain the excitation and emission observations, the energy level scheme was constructed from the calculated electronic structures. The findings in this article could well suggest a new Mg2Si5N8:Eu2+ phosphor with a stable Eu2+ d–f emission and can also be applied to select another rare-earth dopant.

中文翻译：

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来自基态和激发态第一性原理计算的突出 M2Si5N8:Eu2+ 荧光粉（M = Mg、Ca、Sr、Ba）的结构、电子和光学特性

摘要 在本文中，Heyd-Scuseria-Ernzerhof (HSE06) 混合泛函被用来探索 M2Si5N8:Eu2+ 荧光粉（M = Mg、Ca、Sr、Ba）在基态和激发态能级。从纯 M2Si5N8 的电子结构的详细研究来看，价带顶部主要是 Np 特征，计算的带隙与报道的实验值一致。通过 Eu 掺杂，占据的 4f 带直接位于带隙中，导致 4f-5d 字符的光学跃迁。为了确定导带下方 Eu 5d 带的位置，执行了激发态计算。使用导带下方最低激发态 5d 带的位置，计算出的 4f-5d 能隙与实验数据吻合良好。激发态计算证实 Eu2+ d-f 发射将在这些磷光体中占主导地位。此外，为了理解和解释激发和发射观察，从计算的电子结构构建了能级方案。本文中的发现很可能表明一种具有稳定 Eu2+ d-f 发射的新型 Mg2Si5N8:Eu2+ 磷光体，也可用于选择另一种稀土掺杂剂。