Ba 2 Zn 2 B 6 O 13 : coplanar [B 2 O 5 ] in unnoted U-shaped [B 6 O 13 ] groups achieving large birefringence.

Currently, π-conjugated [B 2 O 5 ] moieties are rarely studied for designing deep-UV birefringent crystals. Here, we report a new deep-UV birefringent crystal Ba 2 Zn 2 B 6 O 13 with a deep-UV cut-off edge of 190 nm and large birefringence (Δ n = 0.085@ 532 nm), indicating that it can be used as the birefringent material in the DUV area. The first-principles calculation analyses suggest that its large birefringence mainly originates from the coplanar [B 2 O 5 ] dimers in the unnoted U-shaped [B 6 O 13 ].