Rational combination of multiple structural groups on regulating nonlinear optical property in hexagonal Ln3MGeS7 polar crystals

Abstract

Combination of multiple structural groups was developed as one effective method for regulating material property and exploring new nonlinear optical (NLO) crystals. For that reason, four Ln3MGeS7 (Y3LiGeS7, Y3Cd0.5GeS7, Gd3Cd0.5GeS7 and Sm3Zn0.5GeS7) crystals with various structural motifs were successfully synthesized and systematically investigated. Note that Y3LiGeS7 and Y3Cd0.5GeS7 were firstly synthesized so far. Performance test shows that Ln3MGeS7 compounds exhibit the variable optical bandgaps (1.62–2.33 eV) and good second harmonic generation (SHG) responses (0.7–1.1 × commercial AgGaS2) with requisite phase-matching behavior, which agree well with the theoretical results (Y3LiGeS7: Δn = 0.058 and d33 = 19.97 pm/V; Y3Cd0.5GeS7: Δn = 0.055 and d33 = 20.6 pm/V) and introduction of MIIB (Zn, Cd) atoms into crystal structure is conducive to enlarge the SHG effect. SHG density and dipole-moment calculations indicate that their SHG effects are originated from the major contribution on LnSn units with moderate effect of GeS4 and MIIBS6 (Zn, Cd) ligands. Therefore, selecting appropriate functional motifs (LnSn and MIIB) into crystal structure can promote the enhancement of NLO property and further realize the rational design of new promising infrared NLO materials.