PbGa2GeS6: An Infrared Nonlinear Optical Material Synthesized by an Intermediate-Temperature Self-Fluxing Method

A new non-centrosymmetric (NCS) polar sulfide PbGa2GeS6 has been synthesized by a self-fluxing method at a relatively low temperature of 550 degrees C with desirable properties for nonlinear optical (NLO) applications. Its structure is built by three types of infinite chains intersecting in three dimensions, where the NCS building units are tetragonal pyramids of PbS4 and tetrahedra of MS4 (M = Ga, Ga/Ge). Powder of PbGa2GeS6 exhibits phase matchable (PM) second-order NLO activity with strong second harmonic generation (SHG) intensity of 0.5X AgGaS2 at the particle size of 150-210 mu m, high laser-induced damage threshold (LIDT) of 5X AgGaS2, and a wide transmission range in infrared (IR) region (0.47-23 mu m). First-principles calculations suggest that the macroscopic SHG response is originated from the cooperation of the lone pairs on Pb2+ and MS4 (M = Ga, Ga/Ge) tetrahedra. Considering its strong PM SHG response, high LIDT, wide IR transmission range, and relatively low synthesis temperature, PbGa2GeS6 should be a promising candidate for high-power IR NLO applications.