The Directional Design of the Quasi‐Phase‐Matching Short‐Wave Ultraviolet Nonlinear Optical Crystal

Abstract Since the study of short‐wave ultraviolet nonlinear optical crystals based on the quasi‐phase‐matching principle will effectively expand the development field of nonlinear optical materials, it is urgent to achieve their directional design. Here, it is proposed and implemented on account of the hexagonal wurtzite structure. Thus, the LiRbSeO 4 crystal is obtained with [SeO 4 ] groups as the main tetrahedra and [LiO 4 ] as the separation. It exhibits a wide transparency window (0.22–5.57 µm) and an excellent nonlinear optical effect (≈1.7 × KH 2 PO 4 ), which originates from the synergy of distorted tetrahedral groups and their uniform arrangement. More importantly, the LiRbSeO 4 crystal is confirmed to be a ferroelectric with a typical polarization‐electric field hysteresis loop (a coercive field of 27.71 kV cm −1 , a remanent polarization of 8.60 µC cm −2 at 373 K). Its ferroelectricity is further identified by the domain engineering studies, involving piezoelectricity and the chirality. Besides, ferroelectricity is attributed to the ordered arrangement of tetrahedra with the polarization reversal involving atomic displacements. Therefore, the LiRbSeO 4 crystal is a promising short‐wave ultraviolet nonlinear optical candidate based on the quasi‐phase‐matching principle. This work also provides a new horizon for the design of nonlinear optical crystals.