ABSTRACT Nonlinear optical (NLO) crystals operating in the short‑wavelength ultraviolet (UV) region are essential for all‑solid‑state lasers. For such materials, a moderate birefringence represents a key requirement. Borates with planar π‑conjugated B 3 O 6 rings are promising candidates for short‑wavelength UV NLO crystals, yet their tendency to adopt parallel alignment often leads to excessive birefringence and detrimental beam walk‑off. Herein, we propose a charge‑compensation strategy mediated by heterovalent cation occupation to rationally tailor the arrangement of B 3 O 6 units. Finally, a new noncentrosymmetric crystal that adopts a unique zigzag packing of B 3 O 6 groups distinct from previously reported structural types, RbBaB 3 O 6 , was designed and synthesized. This configuration yields a balanced set of optical properties: a birefringence of 0.075@532 nm, a moderate phase‑matching SHG response, a short UV cutoff edge below 196 nm, and the shortest type‑I phase‑matching wavelength of 236 nm, confirming its potential as a viable UV NLO crystal. This work demonstrates a practical route for fine‑tuning birefringence in borate‑based UV NLO materials, offering a viable candidate for all‑solid‑state laser systems operating in the UV region.
Zhang et al. (2026) studied this question.