KBe2BO3F2 (KBBF) is still the only practically usable crystal that can generate deep‐ultraviolet (DUV) coherent light by direct second harmonic generation (SHG). However, applications are hindered by layering, leading to difficulty in the growth of thick crystals and compromised mechanical integrity. Despite efforts, it is still a great challenge to discover new nonlinear optical (NLO) materials that overcome the layering while keeping the DUV SHG available. Now, two new DUV NLO beryllium borates have been successfully designed and synthesized, NH4Be2BO3F2 (ABBF) and γ‐Be2BO3F (γ‐BBF), which not only overcome the layering but also can be used as next‐generation DUV NLO materials with the shortest type I phase‐matching second‐harmonic wavelength down to 173.9 nm and 146 nm, respectively. Significantly, γ‐BBF is superior to KBBF in all metrics and would be the most outstanding DUV NLO crystal.

Pnictides are superior infrared (IR) nonlinear optical (NLO) material candidates, but the exploration of NLO pnictides is still tardy due to lack of rational material design strategies. An in-depth understanding structure-performance relationship is urgent for designing novel and eminent pnictide NLO materials. Herein, this work unravels a vital band gap mechanism of pnictides, namely P atom with low coordination numbers (2 CN) will cause the decrease of band gap due to the delocalization of non-bonding electron pairs. Accordingly, a general design paradigm for NLO pnictides, ionicity-covalency-metallicity regulation is proposed for designing wide-band gap NLO pnictides with maintained SHG effect. Driven by this idea, millimeter-level crystals of MgSiP2 are synthesized with a wide band gap (2.34 eV), a strong NLO performance (3.5 x AgGaS 2 ), and a wide IR transparency range (0.53-10.3 μm). This work provides an essential guidance for the future design and synthesis of NLO pnictides, and also opens a new perspective at Zintl chemistry important for other material fields.

The rigid planar π-conjugated groups are adopted for designing ultraviolet (UV) nonlinear optical (NLO) materials extensively. However, for these UV NLO crystals, the realization of strong second harmonic generation (SHG)...

A series of new noncentrosymmetric beryllium sulfates, A2BeS2O8 (A = NH4, K, Rb, Cs), were rationally designed and synthesized based on the parent borophosphates KMBP2O8 (M = Sr, Ba). Owing to the rigid three-dimensional frameworks, A2BeS2O8 (A = NH4, K, Rb, Cs) showed the high thermodynamic stabilities. Among them, A2BeS2O8 (A = K, Rb, Cs) exhibited the highest thermodynamic stabilities among all the reported nonlinear (NLO) sulfates. In addition, benefiting from the flexible Be–O bonds within [BeO4], A2BeS2O8 (A = NH4, K, Rb, Cs) exhibited the enhanced second harmonic generation (SHG) responses, which were about 3 to 5 times that of parent borophosphates. Furthermore, they possessed a moderate birefringence of 0.013–0.024 and could be transparent down to the deep ultraviolet (DUV) region below 200 nm. This work indicated that the basic building blocks in borophosphates and beryllium sulfates were potentially interchangeable, which provided the possibility for a further study of new NLO crystals.