Deep-Ultraviolet
Nonlinear Optical Materials: Na<sub>2</sub>Be<sub>4</sub>B<sub>4</sub>O<sub>11</sub> and LiNa<sub>5</sub>Be<sub>12</sub>B<sub>12</sub>O<sub>33</sub>
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Abstract
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 Na<sub>2</sub>Be<sub>4</sub>B<sub>4</sub>O<sub>11</sub> and LiNa<sub>5</sub>Be<sub>12</sub>B<sub>12</sub>O<sub>33</sub> have
been developed through cationic structural engineering. The most closely
arranged [Be<sub>2</sub>BO<sub>5</sub>]<sub>∞</sub> planar
layers, connected by the flexible [B<sub>2</sub>O<sub>5</sub>] 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 Na<sub>2</sub>Be<sub>4</sub>B<sub>4</sub>O<sub>11</sub> and LiNa<sub>5</sub>Be<sub>12</sub>B<sub>12</sub>O<sub>33</sub>, 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 Na<sub>2</sub>Be<sub>4</sub>B<sub>4</sub>O<sub>11</sub> and LiNa<sub>5</sub>Be<sub>12</sub>B<sub>12</sub>O<sub>33</sub> possess very promising
application as deep-UV NLO crystals