Lone pair effects on ternary infrared nonlinear optical materials

• Published in: Physical chemistry chemical physics : PCCP 2019-02, Vol.21 (9), p.5142-5147
• Main Authors: Yin, Ruonan, Hu, Cong, Lei, Bing-Hua, Pan, Shilie, Yang, Zhihua
• Format: Article
• Language: English
• Subjects: Chemical activity; Crystal structure; Crystals; Density functional theory; First principles; Nonlinear optics; Optical materials; Optical properties; Optics; Organic chemistry; Second harmonic generation
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c8cp07894g

First-principles studies of the crystal structures, electronic structures and optical properties of noncentrosymmetrical (NCS) K 3 AsS 4 , Li 3 AsS 3 , Pb 9 As 4 S 15 and Ag 3 AsS 3 have been performed by means of density functional theory. Via a theoretical method to compute the intensity of the lone pair stereochemical activity of an As-S group, the correlated mechanism among the crystal structures, the stereo-chemical activity of lone pairs on As and the second harmonic generation (SHG) response has been clarified. The results prove that the SHG response is not only attributed to the lone pair stereochemical activity of the As-S group but also related to the direction of the forming layers in the crystal structure arrangement. Besides, the quantitative method for the stereo-chemical activity of lone pairs is universal, which is valid for other lone pair systems like those containing Pb 2+ , Bi 3+ , Sn 2+ , etc. The findings facilitate the exploration of materials that may exhibit a relatively large second order NLO reaction and can be used in infrared applications. By incorporating structural factors to compensate for the effects of crystal structure alignment, a quantitative method to estimate the lone pair activity is proposed which indicates that a larger R factor is beneficial to achieve a larger SHG response.