ABSTRACT The development of novel ultraviolet nonlinear optical (UV NLO) materials remains challenging, primarily due to the inherent trade–off among NLO efficiency, bandgap, and birefringence. Herein, we report the first examples of fluorine–containing hybrid lone–pair metal mixed halides UV NLO crystals (C 4 H 8 N 5 ) 2 SbCl 3 F 2 ·H 2 O ( 1 ) and (C 4 H 8 N 5 ) 2 SbCl 2 F 3 ·H 2 O ( 2 ), which exhibit bright blue photoluminescence and wide bandgaps, and their functional motifs’ packing styles exhibit significant difference. The organic (C 4 H 8 N 5 ) + cations in 1 adopt an intersecting arrangement with a large dihedral angle, whereas those in 2 exhibit a displaced parallel stacking pattern, leading to distinct second–harmonic generation (SHG) efficiencies and birefringences. In particular, 2 demonstrates excellent linear and NLO performance, including phase matching behavior with strong SHG response (2.82 × KDP), wide optical bandgap (4.36 eV), and large birefringence (0.23@546 nm), representing the highest SHG response among reported ionic hybrid Sb–based halides with optical bandgap exceeding 4.2 eV. Theoretical and structural studies reveal that the outstanding NLO performance arises from the cooperative effect of distorted SbCl 2 F 3 2 − anions and the uniform alignment of the (C 4 H 8 N 5 ) + cations. This work establishes a design principle for exploring outstanding mixed–halide UV NLO materials.
Wu et al. (Wed,) studied this question.