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Van‐der‐Waals (vdW) deep‐ultraviolet (DUV) nonlinear‐optical (NLO) materials hold great potential to extend DUV NLO applications to two dimensions, but they are rare in nature. In this study, we propose a design principle to realize vdW DUV NLO materials via structural evolution from the non‐vdW (BO3)‐(BeO3F) layers in KBe2BO3F2 (KBBF) to the vdW (BO3)‐(BeO4H) layers in berborite Be2BO5H3 (BBH) and the vdW (BO4)‐(BeO4) layers in beryllium metaborate BeB2O4 (BEBO). Based on first‐principles calculations, the fundamental NLO properties of BBH and BEBO demonstrate that a balanced DUV NLO performance can be achieved in these two systems. Importantly, BBH, a layered material existing in nature, can achieve an available DUV phase‐matched output with strong second harmonic generation (SHG) for 177.3/193.7 nm DUV lasers, which is almost identical to that of KBBF. Remarkably, BEBO shows an excellent DUV SHG capacity and an even shorter phase‐matching wavelength than KBBF. Therefore, the newly discovered vdW BBH and BEBO, once verified by experiments, could provide an ideal platform to study DUV NLO effects in three dimensions and two dimensions. [ABSTRACT FROM AUTHOR]

Deep‐ultraviolet (DUV) nonlinear optical (NLO) crystals are vital to the development of science and state‐of‐the‐art technologies, but the exploration of these important optoelectronic materials is hindered by the contradiction between NLO effect and energy band gap as well as the sensitivity of DUV phase‐matching to optical birefringence. Here, in order to achieve a well balanced DUV NLO performance, we chose the diamond‐like structure as the prototype template for the material design and synthesized the first DUV NLO hydroxycarbonate crystal, LiZn(OH)CO3. This compound simultaneously has a wide band gap (>6.53 eV), a strong second harmonic generation response (ca. 3.2×KDP), and a large birefringence (0.147 at 1064 nm) with the shortest DUV phase‐matching capability (λPM<190 nm) among all reported NLO carbonates. Moreover, the structure–property relationships in LiZn(OH)CO3 are analyzed by first‐principles calculations. This work presents an effective design strategy to push the NLO performance of hydroxycarbonates into the DUV region. [ABSTRACT FROM AUTHOR]