AZn2(BO3)Si2O5 (A = Rb, Cs): first examples of KBe2BO3F2 structure type in the borosilicate family exhibiting a deep-ultraviolet cutoff edge

Abstract

The design and synthesis of nonlinear optical (NLO) crystals are of crucial significance owing to their pivotal role in solid-state lasers. Two dimensional (2D) [Be₂BO₃F₂]_∞ layers in the famous borate fluoride KBe₂BO₃F₂ (KBBF) are a potential source of excellent optical properties, therefore, from structural as well as property aspect KBBF has been employed as a plausible prototype for deep-ultraviolet (DUV) or ultraviolet (UV) NLO crystal design. Herein, the structure of KBBF was extended to the borosilicate system for the first time, and two novel borosilicate NLO crystals AZn₂(BO₃)Si₂O₅ (A = Rb, Cs) with a DUV cutoff edge were synthesized using the high-temperature solution method. In their structures, isolated BO₃ groups and one dimensional (1D) [Si₂O₅]_∞ chains coexist, owing to the connection of the adjacent 2D [Zn₂BO₅]_∞ layers by strong Si–O covalent bond structurally, both compounds can defeat the habit of layered crystal growth. Meanwhile, two compounds display a short UV cutoff edge (down to 190 nm) and possess a moderate second harmonic generation (SHG) response that is approximately 0.4 and 0.8 times that of KDP, respectively. The successful synthesis of AZn₂(BO₃)Si₂O₅ (A = Rb, Cs) may provide novel insights for the discovery of other KBBF structural variants with improved optical performances.