Deep-ultraviolet (DUV, λ < 200 nm) all-solid-state lasers, essential to modern scientific research and industrial manufacturing, are widely applied in fields from material analysis to lithography. Their commercialization depends heavily on high-performance nonlinear optical (NLO) crystals, but developing such crystals is hampered by strict requirements: They must simultaneously possess large second harmonic generation (SHG) responses, moderate birefringence, and wide bandgaps.

Borates have long been a research focus for their exceptional DUV transmission properties. Though materials like β-BBO and LBO have been developed, most cannot achieve DUV phase matching via direct frequency doubling. Fluoroborate systems have emerged as leading candidates due to structural diversity and superior performance, yet existing ones such as KBBF suffer from layered growth habits and toxic raw materials.

Moreover, DUV NLO crystals with chain-like polymerized [BO₃]^3- units are scarce. Thus, designing structural strategies to realize an ordered arrangement of functional units has become key to breaking the performance bottlenecks of DUV NLO materials.