Deep-Ultraviolet Nonlinear Optical Materials: Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃

Deep-UV coherent light generated by nonlinear optical (NLO) materials possesses highly important applications in photonic technologies. Beryllium borates comprising anionic planar layers have been shown to be the most promising deep UV NLO materials. Here, two novel NLO beryllium borates Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ have been developed through cationic structural engineering. The most closely arranged [Be₂BO₅]_∞ planar layers, connected by the flexible [B₂O₅] groups, have been found in their structures. This structural regulation strategy successfully resulted in the largest second harmonic generation (SHG) effects in the layered beryllium borates, which is ∼1.3 and 1.4 times that of KDP for Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃, respectively. The deep-UV optical transmittance spectra based on single crystals indicated their short-wavelength cut-offs are down to ∼170 nm. These results demonstrated that Na₂Be₄B₄O₁₁ and LiNa₅Be₁₂B₁₂O₃₃ possess very promising application as deep-UV NLO crystals