Fluorination‐Driven Molecular Polarization Engineering in Hydroxyfluorooxoborates for Generating Strong Short‐Wavelength Nonlinear Optical Responses

The short‐wavelength ultraviolet (UV, <280 nm) all‐solid‐state lasers, which rely on nonlinear optical (NLO) crystals for second‐harmonic generation (SHG), are of great significance for advanced scientific and industrial. However, the inherent randomness of obtaining non‐centrosymmetric (NCS) structures has long hindered the development of NLO crystals. Herein, we explore novel NLO crystals in the hydrofluorooxoborate system through molecular polarization engineering via a targeted fluorination strategy. Starting from the reported compound CsB 3 O 3 (OH) 3 Cl, partial fluorination was achieved by replacing a hydrogen‐bond donor BO 2 (OH) − group with a [BO 2 F 2 ] 3− group. This substitution breaks the inversion symmetry and leads to the synthesis of two NCS hydrofluorooxoborate, denoted Cs 2 [B 2 O 2 F 2 (OH)]Cl (CBFHC‐I) and Cs 3 [B 3 O 3 F 2 (OH) 2 ]Cl 2 (CBFHC‐II). Both compounds display strong SHG responses (1.1 and 1.4 × KDP, respectively), and CBFHC‐II exhibits a short phase‐matching wavelength down to 243.5 nm. In addition, using the CS Cs[B 3 O 3 F 2 (OH) 2 ] (CBFH) as a parent structural platform, molecular polarization engineering was employed to tune the hydrogen‐bond acceptors, which theoretically proposed a structure Cs[B 3 O 3 F 2 (OH) 2 ] des (CBFH des ) with potentially promising DUV NLO properties (2.4 × KDP, shortest λ pm = 199.2 nm). This work demonstrates the feasibility of exploring short‐wavelength NLO materials by combining fluorination with molecular polarization engineering in hydroxyfluorooxoborates, providing a fresh design avenue for the field.