CsZn2 BO3 X2 (X2 =F2 , Cl2 , and FCl): A Series of Beryllium-Free Deep-Ultraviolet Nonlinear-Optical Crystals with Excellent Properties.

Designing deep-ultraviolet (DUV) nonlinear-optical (NLO) crystals is one of the major current research interests, but it faces a great challenge. In order to overcome the problem of crystal growth and the toxicity of BeO raw materials in KBe2 BO3 F2 (KBBF), the only applicable DUV NLO crystal so far, we substitute Be2+ cations with Zn2+ in the KBBF structure and modify the halogen anions, by which three new Zn-containing KBBF-like compounds, CsZn2 BO3 X2 (X2 =F2 , Cl2 , and FCl), have been successfully synthesized. They all exhibit excellent NLO properties, including improved SHG responses (2.8-3.5×KDP) and short UV cut-off edges (<190 nm). In comparison with KBBF, CsZn2 BO3 X2 (X2 =F2 , Cl2 , and FCl) are all chemically benign and have better growth habits, so they are all promising as DUV NLO crystals. Further study on structure-property relationships indicates that the mixing of halogen anions is a feasible strategy to enhance the SHG responses of the KBBF family.