KREP2S6(RE = Sm, Gd, Tb, Dy): A Series of Polar Rare-Earth Thiophosphates with High Laser-Induced Damage Thresholds and Moderate Nonlinear-Optical Responses Synergistically Contributed by Isolated P2S6Units and {[RE2S15]24–}∞Layers

As one of the potential candidates of nonlinear-optical (NLO) materials, rare-earth chalcophosphates have demonstrated promising properties. Here, KREP2S6(RE = Sm, Gd, Tb, Dy) were synthesized using the facile RE2O3-B-S solid-state method. They crystallize with a monoclinic chiral P21structure, and their layer structures are built by isolated ethane-like P2S6dimers and RES8bicapped trigonal prisms built {[RE2S15]24–}∞layers. By comparing the structures with related ones, the change of the alkali metal or RE3+ions can cause structural transformation. Their band gaps are tunable between 2.58 and 3.79 eV, and their powder samples exhibit good NLO properties. Theoretical calculations suggest that the NLO properties are mainly contributed by P2S6units and {[RE2S15]24–}∞layers synergistically, in which {[RE2S15]24–}∞layers and P2S6units dominate the contribution to the band gap and second-harmonic-generation response, respectively. This work enriches the application of rare-earth chalcophosphates as NLO materials.