Honeycomb layered topology construction for exceptional long-wave infrared nonlinear optical crystals

Nonlinear optical (NLO) crystals capable of efficient long-wave infrared (8-14 μm) laser output remain scarce, and the exploration of long-wave IR NLO materials with superior comprehensive optical performances is a momentous challenge. Herein, we develop two selenide-halide NLO crystals, Hg₃AsSe₄Br and Hg₃AsSe₄I, which are derived from the honeycomb layered topology of prototype GaSe. Remarkably, they exhibit not only strong SHG effects, suitable band gap, large birefringence, broad IR transparency range and low two-photon absorption coefficients but reinforced interlayer interaction and more benign crystal growth habit, compared to those of GaSe, indicating that they are promising long-wave IR NLO materials. Moreover, Hg₃AsSe₄I achieved better comprehensive optical properties than conventional IR crystals, GaSe, ZnGeP₂, CdSe and AgGaSe₂. The idea of honeycomb layered topology construction provides a material design heuristic to explore cutting-edge IR NLO materials.