[C(NH_(2))3]3PO_(4)·2H_(2)O:一种具有大双折射和大倍频响应的新型无金属紫外磷酸盐非线性光学晶体

[C(NH)]PO·2HO: A new metal-free ultraviolet nonlinear optical phosphate with large birefringence and second-harmonic generation response

[PO_(4)]3-具有较小的微观二阶极化率和极化各向异性,这往往导致磷酸盐具有较小的倍频效应和双折射率.本文采用溶液蒸发法设计并合成了新型非中心对称磷酸盐[C(NH_(2))3]3PO_(4)·2H_(2)O.无金属离子的[C(NH_(2))3]3PO_(4)·2H_(2)O由平面共轭胍阳离子和磷酸根四面体组成,并通过氢键连接形成三维网络.物理性能测量表明,与大多数报道的紫外非线性光学材料中的磷酸盐相比,标题化合物显示出更大的双折射(0.055@546.1 nm)和大倍频响应(1.5×KDP).此外,第一性原理计算表明,π共轭的平面[C(NH_(2))3]+阳离子和[PO_(4)]3-基团是其优异的线性和非线性光学特性的来源.

[PO_(4)]3-possesses small microscopic secondorder susceptibility and polarizability anisotropy,which inherently result in weak second-harmonic generation (SHG)and small birefringence.Herein,a new noncentrosymmetric phosphate,[C(NH_(2))3]3PO_(4)·2H_(2)O,was successfully designed and synthesized by a solution evaporation method.[C(NH_(2))3]3PO_(4)·2H_(2)O without metal ions is composed of planar conjugated guanidine cations and PO_(4)tetrahedrons,which are connected by hydrogen bonds,forming a three-dimensional network.Physical property measurements indicate that the title compound displays an SHG response of 1.5×KH_(2)PO_(4)(KDP) and a larger birefringence (0.055@546.1 nm)compared with most reported ultraviolet nonlinear optical phosphates.Furthermore,first-principles calculations reveal that theπ-conjugated planar[C(NH_(2))3]+cations and[PO_(4)]3-groups are responsible for its excellent linear and NLOproperties.