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

The dearth of suitable materials significantly restricts the practical development of infrared (IR) laser systems with highly efficient and broadband tuning. Recently, gamma-NaAsSe2 is reported, and it exhibits a large nonlinear second-harmonic generation (SHG) coefficient of 590 pm V-1 at 2 mu m. However, the crystal growth of gamma-NaAsSe2 is challenging because it undergoes a phase transition to centrosymmetric delta-NaAsSe2. Herein, the stabilization of non-centrosymmetric gamma-NaAsSe2 by doping the As site with Sb, which results in gamma-NaAs0.95Sb0.05Se2 is reported. The congruent melting behavior is confirmed by differential thermal analysis with a melting temperature of 450 degrees C and crystallization temperature of 415 degrees C. Single crystals with dimensions of 3 mm x 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 gamma-NaAs0.95Sb0.05Se2 exhibits an enormous value of |d(11)| = 648 +/- 74 pm V-1, which is comparable to that of gamma-NaAsSe2 and approximate to 20x larger than that of AgGaSe2. The bandgap of gamma-NaAs0.95Sb0.05Se2 (1.78 eV) is similar to that of AgGaSe2, thus rendering it highly attractive as a high-performing nonlinear optical material.