Exploration of new infrared (IR) nonlinear optical (NLO) materials is still in urgency owing to the indispensable roles in optoelectronic devices, resource exploration, and long-distance laser communication. The formidable challenge is to balance the contradiction between wide band gaps and large second harmonic generation (SHG) effects in IR NLO materials. In the present work, we proposed new kinds of NLO active units, d⁰ transition metal fluorooxo-functional groups for designing mid-IR NLO materials. By studying a series of d⁰ transition metal oxyfluorides (TMOFs), the influences of fluorooxo-functional groups with different d⁰ configuration cations on the band gap and SHG responses were explored. The results reveal that the fluorooxo-functional groups with different d⁰ configuration cations can enlarge band gaps in mid-IR NLO materials. The first-principles calculations demonstrate that the nine alkali/alkaline earth metals d⁰ TMOFs exhibit wide band gaps (all the band gaps > 3.0 eV), large birefringence Δn (> 0.07), and two W/Mo TMOFs also exhibit large SHG responses. Moreover, by comparing with other fluorooxo-functional groups, it is found that introducing fluorine into building units is an effective way to enhance optical performance. These d⁰ TMOFs with superior fluorooxo-functional groups represent a new exploration family of the mid-IR region, which sheds light on the design of mid-IR NLO materials possessing large band gap.

由于在光电器件，资源勘探和长距离激光通信中不可或缺的作用，因此对新的红外（IR）非线性光学（NLO）材料的探索仍然迫在眉睫。艰巨的挑战是要在IR NLO材料中平衡宽带隙和较大的二次谐波产生（SHG）效应之间的矛盾。在目前的工作中，我们提出了新型的NLO活性单元，d ⁰过渡金属氟代氧官能团，用于设计中红外NLO材料。通过研究一系列的d ⁰过渡金属氟氧化物（TMOF），研究了不同d ⁰的氟代氧官能团的影响探索了带隙和SHG响应上的构型阳离子。结果表明，具有不同d ⁰构型阳离子的氟代氧官能团可以扩大中红外NLO材料的带隙。第一性原理计算表明，九种碱金属/碱土金属d ⁰ TMOF具有较宽的带隙（所有带隙> 3.0 eV），大双折射Δn（> 0.07）和两个W / Mo TMOF也具有较大的SHG回应。此外，通过与其他氟代氧官能团进行比较，发现将氟引入建筑单元是增强光学性能的有效方法。这些d ⁰ 具有优异的氟代氧官能团的TMOF代表了中红外区域的一个新的探索家族，这为具有较大带隙的中红外NLO材料的设计提供了启示。