LnLiSiS4 (Ln = La and Ce): Promising infrared nonlinear optical materials designed by aliovalent substitution from SrCdSiS4

Aliovalent substitution is an effective route to design new nonlinear optical (NLO) crystals. Using SrCdSiS4 as a parent compound, two new infrared NLO lanthanide thiosilicates, namely LnLiSiS4 (Ln = La and Ce), have been successfully obtained through aliovalent substitution. Interestingly, these compounds exhibit [LiSiS4]3- layers composed of vertex- and edge-shared LiS4 and SiS4 tetrahedra that significantly different from the [LnSiS4]3- layers composed of edge-shared LnS6 trigonal prisms (or LnS7 monocapped trigonal prisms) and SiS4 tetrahedra in other ALnSiS4 (A = K, Rb, Cs, Ln = lanthanide) compounds with larger sized alkali cations. LnLiSiS4 (Ln = La and Ce) also achieve balanced properties for good infrared NLO materials: largest SHG response among all known thiosilicates (2.0 and 2.1 × AgGaS2 @ 2 μm for LaLiSiS4 and CeLiSiS4 respectively) with phase matching ability, high laser induced damage threshold (14 and 9 times of AgGaS2), wide bandgap (3.71 and 2.92 eV), wide infrared transmission range (0.35–18 μm) and good thermal stability above 700 °C. This work not only enriches the structure chemistry of lanthanide thiosilicates, but also provides an efficient route to design new high performance IR NLO materials.