KREP2Se6 (RE = Sm, Gd, Tb): The First Rare‐Earth Selenophosphates with Remarkable Nonlinear Optical Activities Realized by Synergistic Effect of RE‐ and P‐Based Motifs

Rare-earth (RE) chalcogenides have been extensively studied as infrared nonlinear optical (NLO) materials because of their nice integrated performances; however, very few RE chalcophosphates are involved for this topic. Here, three quaternary RE selenophosphates, KSmP2 Se6 (1), KGdP2 Se6 (2), and KTbP2 Se6 (3), are profoundly studied for their NLO potentials. Their noncentrosymmetric P21 structures feature RESe8-bicapped trigonal prisms and ethane-like [P2 Se6 ]4 - dimers built {[REP2 Se6 ]-}∞ layers. As the first studied NLO-active RE selenophosphates, 1-3 exhibit second harmonic generation (SHG)responses ≈0.34-1.08 × AgGaS2 at 2.10 µm and laser-induced damage thresholds (LIDTs) ≈1.43-4.33 × AgGaS2 , and they all show phase-matchable behaviors, indicating their wonderful balanced NLO properties. Theoretical calculations demonstrate that the synergistic effect between RESe8 and P2 Se6 units makes the major contribution to the SHG responses.