Two noncentrosymmetric (NCS) quaternary selenides, PbGa2SiSe6 (<bold>1</bold>) and PbGa2GeSe6 (<bold>2</bold>), with second-order nonlinear optical (NLO) responses, were synthesized by a conventional high-temperature solid-state reaction method. Compounds <bold>1</bold> and <bold>2</bold> are constructed by three NCS chromophores, [PbSe4], [GaSe4], and [Ga/SiSe4] or [Ga/GeSe4], with the covalent interactions between the X and Se atoms (X = Pb, Ga, Ga/Si, or Ga/Ge). They crystallize in the polar space groups Cc and Fdd2, respectively. Inspiringly, compound <bold>2</bold> is phase-matchable (PM) and shows high laser-induced damage threshold (LIDT) of 3.7 x AgGaS2 and wide transparent region (0.6325 mu m) in the mid-infrared (MIR) region. Most importantly, it presents extraordinary strong second harmonic generation (SHG) at 2.05 mu m radiation of about 12 x AgGaS2 at the particle size of 2545 mu m, which represents the strongest SHG among PM chalcogenides to date. The calculated major SHG tensor elements of compounds <bold>1</bold> and <bold>2</bold> are d31 = 224.7 and d12 = 222.1 pm/V, respectively, while the calculated d36 of AgGaS2 is only 21.2 pm/V.
2015. Vol. 27, no 3, 914-922 p.