Ba2MAsQ5 (Q = S and Se) Family of Polar Structures with Large Second Harmonic Generation and Phase Matchability

摘要

Noncentrosymmetric chalcogenides containing ster-eochemically active lone pair elements, such as As, Sb, and Bi, offera useful way to tune the band gap and enhance the secondharmonic generation (SHG) response. Ba2As_(2-x).Sb_xQ5,Ba2As_(2-x).Bi_x.Q5 (Q = S and Se), and Ba2As2S_(4.8)Se_(0.2) are newchalcoarsenates that crystallize in the noncentrosymmetricmonoclinic space group P2_l. These five new compoundscrystallized with a three-dimensional (3D) Ba2As2Se5-typestructure, containing AsQ3 units and As2Q4~(2-) dimeric units.The As2Q~(2-) dimeric unit can be tuned by replacing As with Sb or Bi and Se with S. In contrast, Ba2As2S5 crystallizes in theorfhorhombic space group P_(ca)2_1. Differential thermal analysis suggested that Ba2As2S5, Ba2As2Se5, Ba2AsSbSe5, and Ba2As_(1.25)Bi_(0.75)Se5melt congruently. The M2Q4~(2-) unit plays a significant role in tuning the band gap of these compounds, decreasing from 2.02 eV inBa2As2S5 to 1.37 eV in Ba2As_(1.25)Bi_(0.75)Se5. Powder SHG measurements showed all the compounds are essentially phase-matchable at3300 nm. Ba2AsSbSe5 exhibits the highest X~((2)) of 36 pm/V and a laser-induced damage threshold of 0.10 GW/cm~2, comparable tothat of AgGaQ2. These materials show significantly improved SHG behavior response to BaGa4Q7 compounds, making themattractive for commercial applications.