Stabilization of the Polar Structure and Giant Second‐Order Nonlinear Response of Single Crystal γ‐NaAs_0.95Sb_0.05Se₂

Abstract

Abstract The dearth of suitable materials significantly restricts the practical development of infrared (IR) laser systems with highly efficient and broadband tuning. Recently, γ‐NaAsSe 2 is reported, and it exhibits a large nonlinear second‐harmonic generation (SHG) coefficient of 590 pm V −1 at 2 µm. However, the crystal growth of γ‐NaAsSe 2 is challenging because it undergoes a phase transition to centrosymmetric δ‐NaAsSe 2 . Herein, the stabilization of non‐centrosymmetric γ‐NaAsSe 2 by doping the As site with Sb, which results in γ‐NaAs 0.95 Sb 0.05 Se 2 is reported. The congruent melting behavior is confirmed by differential thermal analysis with a melting temperature of 450 °C and crystallization temperature of 415 °C. Single crystals with dimensions of 3 mm × 2 mm are successfully obtained via zone refining and the Bridgman method. The purification of the material plays a significant role in crystal growth and results in a bandgap of 1.78 eV and thermal conductivity of 0.79 Wm −1 K −1 . The single‐crystal SHG coefficient of γ‐NaAs 0.95 Sb 0.05 Se 2 exhibits an enormous value of | d 11 | = 648 ± 74 pm V −1 , which is comparable to that of γ‐NaAsSe 2 and ≈20× larger than that of AgGaSe 2 . The bandgap of γ‐NaAs 0.95 Sb 0.05 Se 2 (1.78 eV) is similar to that of AgGaSe 2 , thus rendering it highly attractive as a high‐performing nonlinear optical material.