Cation-Tuned Synthesis of Fluorooxoborates: Towards Optimal Deep-Ultraviolet Nonlinear Optical Materials.

The development of new nonlinear optical (NLO) materials for deep-ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali-metal fluorooxoborates, AB4 O6 F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2 PO4 (KDP). Interestingly, by judicious selection of the A-site alkali-metal cations, the arrangement of NLO-active structural units is fine-tuned to an optimal configuration, which contributes to large SHG responses.