KREP2 Se6 (RE = Sm, Gd, Tb): The First Rare-Earth Selenophosphates with Remarkable Nonlinear Optical Activities Realized by Synergistic Effect of RE- and P-Based Motifs

Abstract

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.

Keywords: crystal structure; laser-induced damage threshold selenophosphate; nonlinear optics; rare earth; selenophosphate.