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Van der Waals (vdW) deep‐UV (DUV) nonlinear optical (NLO) crystal is an important material system recently developed. Herein, we review its concept and original intention, and then summarized the discovery process of related materials, including the role of A‐site cations and the resulting two‐/one‐dimensional vdW DUV NLO systems. Finally, we evaluate the practical DUV NLO performance and prospected the opportunities and challenges. [ABSTRACT FROM AUTHOR]

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]

A novel concept to obtain the deep‐ultraviolet (DUV) nonlinear optical (NLO) materials is proposed based on the assembling of one‐dimensional (1D) polar motifs into quasi‐1D polymer patterns. Based on the first‐principles calculations, we have successfully discovered an excellent DUV NLO polymer, i.e. poly(difluorophosphazene), with the chemical formula of (PNF2)n. Calculations reveal that PNF2 has a larger band gap, a stronger second harmonic generation effect, a larger birefringence, and a shorter phase‐matching cutoff than KBe2BO3F2. These findings not only demonstrate that the PNF2 is the first reported DUV NLO polymer, but also could open a new direction to discover novel DUV NLO materials in polymer systems. [ABSTRACT FROM AUTHOR]

In this work, we propose a strategy to design new deep‐ultraviolet (deep‐UV) nonlinear optical (NLO) materials through the combination of borate and phosphate NLO material genome. Accordingly, a series of borophosphates are predicted with very large energy bandgaps, strong second harmonic generation (SHG) effects, and moderate birefringence in the deep‐UV region. In particular, two novel fluoride borophosphates, PBO3F2 and PB3O6F2, are able to achieve the deep‐UV SHG laser output with shorter phase‐matching wavelengths (≈155 and 137 nm) than that of KBe2BO3F2 (KBBF, ≈161 nm). Further calculations show that these two structures are dynamically and thermodynamically stable, thus triggering possible synthesis, growth, and applications of them. The results attest that the proposed strategy is instructive and pave a comprehensive road map for us to discover new NLO crystals, especially in the borophosphate catalog with excellent deep‐UV phase‐matching capabilities beyond KBBF. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

A computer-assisted material design system based on first-principles DFT calculations is employed to predict that NH4Be2BO3F2 possesses nonlinear optical properties, such as deep-UV second harmonic generation capability, very close to those of KBe2BO3F2. [ABSTRACT FROM AUTHOR]

The non-linear optical (NLO) material BiB2O4F is prepared by hydrothermal synthesis employing a 1:20:2 molar mixture of Bi(NO3)3, H3BO3, and NaF (autoclave, 200 °C, 3 d, ≈90% yield). [ABSTRACT FROM AUTHOR]