Alkali Metal Substitution-Induced Structural Transformation for RbREP2Se6 (RE = Gd, Tb, Dy) with Second-Harmonic Generation Responses
来源：ACS Publications
Rare-earth (RE) chalcogenides have been extensively studied as infrared nonlinear optical (NLO) materials, and they demonstrate high potential as candidates with integrated performances; however, the subgroup of RE chalcophosphates has been rarely studied. Herein, three new quaternary RE selenophosphates, RbGdP2Se6 (1), RbTbP2Se6 (2), and RbDyP2Se6 (3), were synthesized using the reactive flux RbI-assisted RExOy–B–Se solid-state method. They crystallize in the orthorhombic chiral space group P212121 and are the first RE chalcophosphate NLO materials crystallizing in this space group. Their structures feature {[REP2Se6]−}∞ layers constructed by RESe8 bicapped trigonal prisms and ethane-like P2Se6 dimers. 1–3 exhibit phase-matchable SHG responses of ∼0.2–0.3 × AgGaS2 at 2.10 μm and optical bandgaps of ∼2.40–2.51 eV. Theoretical calculations reveal that the synergistic effect between the RESe8 and P2Se6 motifs contributes to the SHG responses.