LaSiP<sub>3</sub> and LaSi<sub>2</sub>P<sub>6</sub>: Two Excellent Rare‐Earth Pnictides with Strong SHG Responses as Mid‐ and Far‐Infrared Nonlinear Optical Crystals
Yingshuang Sun, Jindong Chen, Shunda Yang, Bingxuan Li, Guoliang Chai, Chensheng Lin, Min Luo, Ning Ye
Abstract
Abstract Two rare‐earth pnictide‐based infrared (IR) nonlinear optical (NLO) crystals, LaSiP 3 and LaSi 2 P 6 , are successfully synthesized by metal salt flux method, which are the first two cases for rare‐earth pnictides as IR NLO crystals. LaSiP 3 ( Pna 2 1 ) features 2D structure consisting of alternately stacked SiP 4 tetrahedra layers and isolated PP chains. LaSi 2 P 6 ( Cmc 2 1 ) has a 3D structure composed of two types of SiP 4 tetrahedra layers and diversiform phosphorous polyanions. Particularly, LaSi 2 P 6 exhibits the largest second‐order NLO coefficient ( d 33 = 98.5 pm V −1 ) among the known IR NLO phosphides. Besides, LaSiP 3 and LaSi 2 P 6 both can achieve phase matching, cover wide IR transparent regions, and own large birefringence (0.24 and 0.25 @2050 nm for LaSiP 3 and LaSi 2 P 6 , respectively). The studies on LaSiP 3 and LaSi 2 P indicate that they are potentially applied in the middle‐ and far‐IR regions. In addition, more importantly, the theoretical calculations uncover the second‐harmonic‐generation enhancement mechanisms for PP bonds in different forms, which highlight that either PP chains or phosphorous polyanions will be excellent NLO‐active units for constructing high‐performance IR NLO crystals.