An Unprecedented [BO<sub>2</sub>]‐Based Deep‐Ultraviolet Transparent Nonlinear Optical Crystal by Superhalogen Substitution
Shuai Liu, Xingxing Jiang, Qi Lu, Yilei Hu, Kaining Duanmu, Chao Wu, Zheshuai Lin, Zhipeng Huang, Mark G. Humphrey, Chi Zhang
Abstract
Abstract Solid‐state structures with the superhalogen [BO 2 ] − have thus far only been observed with a few compounds whose syntheses require high reaction temperatures and complicated procedures, while their optical properties remain almost completely unexplored. Herein, we report a facile, energy‐efficient synthesis of the first [BO 2 ]‐based deep‐ultraviolet (deep‐UV) transparent oxide K 9 [B 4 O 5 (OH) 4 ] 3 (CO 3 )(BO 2 ) ⋅ 7H 2 O (KBCOB). Detailed structural characterization and analysis confirm that KBCOB possesses a rare four‐in‐one three‐dimensional quasi‐honeycomb framework, with three π‐conjugated anions ([BO 2 ] − , [BO 3 ] 3− , and [CO 3 ] 2− ) and one non‐π‐conjugated anion ([BO 4 ] 5− ) in the one crystal. The evolution from the traditional halogenated nonlinear optical (NLO) analogues to KBCOB by superhalogen [BO 2 ] − substitution confers deep‐UV transparency (<190 nm), a large second‐harmonic generation response (1.0×KH 2 PO 4 @ 1064 nm), and a 15‐fold increase in birefringence. This study affords a new route to the facile synthesis of functional [BO 2 ]‐based oxides, paving the way for the development of next‐generation high‐performing deep‐UV NLO materials.