Reactive flux assisted metal oxide–boron–sulfur routine for syntheses of CsRESiS4 (RE = Sm, Gd–Ho): featuring nonlinear optical activity and wide band gaps

The study of infrared nonlinear optical (NLO) materials with wide band gaps and high laser induced damage thresholds (LIDTs) is an urgent and challenging topic. Here, we report the NLO properties of CsRESiS4 (RE = Sm, Gd–Ho), which were synthesized by the reactive flux CsCl assisted RExOy–B–S routine. The structure of CsRESiS4, [CsS7] pentagonal bipyramids are orderly arranged to populate the interlayer space created by [RES7] monocapped triangular prisms consolidated [SiS4] tetrahedra. They all exhibit wide band gaps of 3.51–3.95 eV, high LIDTs of 3.6–5.5 × AGS, and NLO activity, with CsHoSiS4 possessing the largest band gap among rare-earth chalcogenides. The theoretical calculation results indicate that [RES7] monocapped triangular prisms are the main source of NLO activity and have a wide band gap. This work provides an effective case for exploring wide band gap infrared NLO materials.