Alkali Metal Substitution-Induced Structural Transformation for RbREPSe (RE = Gd, Tb, Dy) with Second-Harmonic Generation Responses.

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, RbGdPSe (), RbTbPSe (), and RbDyPSe (), were synthesized using the reactive flux RbI-assisted REO-B-Se solid-state method. They crystallize in the orthorhombic chiral space group 222 and are the first RE chalcophosphate NLO materials crystallizing in this space group. Their structures feature {[REPSe]} layers constructed by RESe bicapped trigonal prisms and ethane-like PSe dimers. - exhibit phase-matchable SHG responses of ∼0.2-0.3 × AgGaS at 2.10 μm and optical bandgaps of ∼2.40-2.51 eV. Theoretical calculations reveal that the synergistic effect between the RESe and PSe motifs contributes to the SHG responses.