A Promising Deep Ultraviolet Nonlinear Optical Crystal Activated by the Ordered Structure Design

Deep-ultraviolet nonlinear optical (DUV NLO) crystals play a vitally important role in many scientific and technological fields, yet their rational design remains an ongoing challenge. Here, through utilizing the ordered structure design, a new KBe₂BO₃F₂-like DUV transparent NLO crystal Cs₂KY(B₃O₆)₂ has been successfully designed and synthesized, in which we first use the largest π-conjugated B₃O₆ functional groups to substitute the BO₃ to maximize the second-harmonic generation (SHG) response and utilize the K/YO₆ connecting groups to replace two BeO₃F groups to optimize the layer connections. Eventually, Cs₂KY(B₃O₆)₂ exhibits not only the largest SHG responses in KBe₂BO₃F₂-like DUV borates but also the best growth rate along c axis (the strong layer-habit along c axis has been being the greatest obstacle to prohibit the practical application of KBe₂BO₃F₂ and its derivative). Clearly, the substitution from BO₃ triangles to similar topological B₃O₆ groups and from (BeO₃F)₂ groups to similar topological K/YO₆ octahedra can better modulate the functional properties of materials in the larger scale. That results in the superior comprehensive properties of Cs₂KY(B₃O₆)₂ and makes it a promising DUV NLO crystal. Therefore, the ordered structure design provides some new insights for assembling the functional and connecting groups to rationally design materials with high-performance.