Qiang Wang,Wen Song,Yang Lan,Liling Cao,Ling Huang,Daojiang Gao,Jian Bi,Guohong Zou
KBe2BO3F2 (KBBF) with a perfect honeycomb hexagonal layered structure is the sole practical deep-ultraviolet (DUV) nonlinear optical material which could generate DUV coherent light through direct frequency doubling. However, the layered growth habit and the toxicity of Be severely hinder its extensive applications. Herein, a non-centrosymmetric fluoride carbonate, KLi2CO3F, was successfully developed via chemical co-substitution with KBBF as the prototype. KLi2CO3F preserves the structural merits of KBBF, containing neatly arranged infinite planar [Li2CO3F2]∞ layers. In particular, compared with the weak interlayer K–F electrostatic attraction in KBBF, KLi2CO3F presents a stronger interlayer binding energy induced by the shorter and stronger Li–F bonds, which effectively overcomes the layered tendency of crystal growth. Simultaneously, KLi2CO3F exhibits a large birefringence of approximately 0.102@546 nm and a short ultraviolet absorption edge down to 190 nm, indicating that it is a promising DUV birefringent material.
Yaoguo Shen,Sangen Zhao,Yi Yang,Liling Cao,Zujian Wang,Bingqing Zhao,Zhihua Sun,Zheshuai Lin,Junhua Luo
A new beryllium-free borate Rb3Ba3Li2Al4B6O20F features a layered structure analogous to that of the solely available deep-ultraviolet nonlinear optical (NLO) material KBe2BO3F2 (KBBF), and thus preserves its outstanding linear and nonlinear optical properties to a great extent. Furthermore, the interlayer bonding in Rb3Ba3Li2Al4B6O20F is significantly reinforced, with a magnitude of more than 15.6 times that of KBBF. As a result, a bulk Rb3Ba3Li2Al4B6O20F crystal is successfully grown in the preliminary experiments. The result demonstrates that the Rb3Ba3Li2Al4B6O20F crystal may have no (or only a tiny) layering growth habit, which severely hinders the practical applications of KBBF. Notably, Rb3Ba3Li2Al4B6O20F overcomes the structural instability problem present in the notable KBBF-family member Sr2Be2B2O7. These results make Rb3Ba3Li2Al4B6O20F a promising candidate for the next generation of deep-ultraviolet NLO materials. First-principles calculations are performed to elucidate the optical properties and structural stability.
Deep-ultraviolet (DUV) nonlinear optical (NLO) crystals that can extend the output range of coherent light below 200 nm are pivotal materials for solid-state lasers. To date, KBe2BO3F2 (KBBF) is the only usable crystal that can generate DUV coherent light by direct second harmonic generation (SHG), but the layered growth habit and toxic ingredients limit its application. Herein, we report a new fluoroborophosphate, (NH4)3B11PO19F3 (ABPF), containing four different functional units: [BO3], [BO4], [BO3F] and [PO4]. ABPF exhibits a KBBF-like structure while eliminating the limitations of KBBF crystal. The unique [B5PO10F]∞ layers enhance ABPF’s performance; for example, it has a large SHG response (1.2 × KDP) and a sufficient birefringence (0.088 at 1064 nm) that enables the shortest phase-matching wavelength to reach the DUV region. Meanwhile, the introduction of strong B-O-P covalent bonds decreases the layered growth habit. These findings will enrich the structural chemistry of fluoroborophosphate and contribute to the discovery of more excellent DUV NLO crystals.
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