KYSiSe4: A Rare-Earth Selenide Infrared Nonlinear Optical Crystal with Wide Infrared Transparency and Well-Balanced Eg and SHG Response

Infrared (IR) nonlinear optical (NLO) crystals as frequency-conversion devices have shown wide applications in military and civil region. Rare-earth chalcogenides have emerged as a promising IR NLO crystal resource. To realize wide IR transparent ranges, wide bandgaps, and large NLO effects, K⁺ with high electropositivity, light rare earth cation Y³⁺ were induced into the selenide system. Fortunately, KYSiSe₄, a rare-earth selenide with a wide IR transparent range (0.38-20.5 μm) and well-balanced E_g (3.25 eV) and SHG response (0.70 × AgGaS₂) was obtained. First-principles analysis revealed that NLO properties were mainly due to the joint contribution of [SiSe₄] anionic groups and [YSe₇] polyhedra. This work indicates that KYSiSe₄ may be regarded as a potential IR NLO candidate.