A Rare Earth Chalcogenide Nonlinear Optical Crystal KLaGeS<sub>4</sub>: Achieving Good Balance among Band Gap, Second Harmonic Generation Effect, and Birefringence
Yang Liu, Xiangming Li, Shuchang Wu, Mengjie Ma, Xiao‐Ming Jiang, Yuandong Wu, Dajiang Mei
Abstract
Midinfrared nonlinear optical (NLO) rare earth chalcogenides have attracted extensive research interest in recent several decades. Employing charge-transfer engineering strategy in the early stage, rigid tetrahedral [GeS 4 ] was introduced into rare-earth sulfides to synthesize KYGeS 4, which had an enlarged band gap while maintaining a strong second harmonic generation (SHG) effect. Based on KYGeS 4, La was equivalently substituted to successfully synthesize KLaGeS 4 with a stronger SHG effect ( d ij = 1.2 × AgGaS 2 ) and lower cost. Meanwhile, a larger band gap ( E g = 3.34 eV) was retained and realized phase matching (Δ n = 0.098 @ 1064 nm). KLaGeS 4 enabled an effective balance among band gap, SHG effect, and birefringence, making it a promising candidate for infrared NLO optical materials among various rare-earth sulfides.