Remarkable phase-matchable second-harmonic generation realized by strong polarities of [PbSe3] and [GaSe4] functional motifs in PbGa4Se7
Strong second-harmonic generation (SHG) and phase-matchable capability at specific transmittance windows are crucial to the real application of nonlinear optical crystals. Herein, an efficient strategy of introducing Pb 2+ with stereochemically active lone-pair electrons into non-phase-match-able Ga 2 Se 3 via enhancing the anisotropy microstructure is first applied to meet phase-matchable SHG intensity requirements, offering a selenide, namely, PbGa 4 Se 7 , which is designed and synthesized with a diamond-like anionic framework, where Pb 2+ cations reside in a parallel arrangement. As expected, PbGa 4 Se 7 possesses a large SHG coefficient of 3.3 times that of AgGaS 2 under the incident laser of 1910 nm. Moreover, PbGa 4 Se 7 displays a high laser-induced damage threshold of 7.0 times that of AgGaS 2 at 2090 nm, which originates from the low anisotropy of thermal expansion coefficient (0.36) and suitable optical band gap (2.1 eV). Theoretical calculations demonstrate that the considerable phase-matchable SHG response of PbGa 4 Se 7 can be attributed to the synergies of tetrahedral GaSe 4 and pyramid PbSe 3 microstructural blocks with additional anisotropy and polarizability.
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