Stabilization of the Polar Structure and Giant Second‐Order Nonlinear Response of Single Crystal γ‐NaAs0.95Sb0.05Se2

Abstract

AbstractThe dearth of suitable materials significantly restricts the practical development of infrared (IR) laser systems with highly efficient and broadband tuning. Recently, γ‐NaAsSe2 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‐NaAsSe2 is challenging because it undergoes a phase transition to centrosymmetric δ‐NaAsSe2. Herein, the stabilization of non‐centrosymmetric γ‐NaAsSe2 by doping the As site with Sb, which results in γ‐NaAs0.95Sb0.05Se2 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‐NaAs0.95Sb0.05Se2 exhibits an enormous value of |d11| = 648 ± 74 pm V−1, which is comparable to that of γ‐NaAsSe2 and ≈20× larger than that of AgGaSe2. The bandgap of γ‐NaAs0.95Sb0.05Se2 (1.78 eV) is similar to that of AgGaSe2, thus rendering it highly attractive as a high‐performing nonlinear optical material.