Zhang Wenbin, Huang Junben, Han Shujuan, Yang Zhihua, Pan Shilie
CAS Key Laboratory of Functional Materials and Devices for Special Environments, Xinjiang Technical Institute of Physics & Chemistry, CAS, Xinjiang Key Laboratory of Electronic Information Materials and Devices, 40-1 South Beijing Road, Urumqi 830011, China.
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
J Am Chem Soc. 2022 May 25;144(20):9083-9090. doi: 10.1021/jacs.2c02310. Epub 2022 May 13.
Borophosphates are very known for the short ultraviolet (UV) cutoff edge and have become the promising UV and deep-UV functional crystals candidates; however, tetrahedral [PO] and [BO] groups own weak anisotropy of polarizability and are not conducive to large birefringence, which hinders their application in the short-wavelength region. Improving their birefringence without compromising the band gap is the main research objective. By introducing the excellent birefringent functional groups, such as [BO], [BO] chain, [BO(OH)], and so forth into borophosphates, seven borophosphates with improved birefringence were successfully synthesized (Δ > 0.05@532 nm). Remarkably, among them, the centimeter-sized crystal of RbBPO with a short deep-UV cutoff edge (175 nm) and large birefringence (Δ ∼ 0.072@589.3 nm) exhibits the shortest phase-matching wavelength (222 nm), which makes RbBPO a promising UV NLO crystal, while KBPO(OH) with deep-UV cutoff edge features the largest birefringence (Δ ∼ 0.103@546 nm) in the reported borophosphate system, making KBPO(OH) a promising deep-UV birefringent crystal. This study not only provides feasible strategies for increasing the birefringence of borophosphates but also pushes phase-matching into the short-wavelength region.
硼磷酸盐因其短紫外截止边而广为人知，并已成为有前景的紫外和深紫外功能晶体候选材料；然而，四面体[PO]和[BO]基团的极化率各向异性较弱，不利于产生大双折射，这阻碍了它们在短波长区域的应用。在不降低带隙的情况下提高其双折射是主要研究目标。通过将优异的双折射功能基团，如[BO]、[BO]链、[BO(OH)]等引入硼磷酸盐中，成功合成了七种双折射得到改善的硼磷酸盐（在532nm处Δ>0.05）。值得注意的是，其中具有短深紫外截止边（175nm）和大双折射（在589.3nm处Δ0.072）的厘米级RbBPO晶体表现出最短的相位匹配波长（222nm），这使得RbBPO成为一种有前景的紫外非线性光学晶体，而具有深紫外截止边的KBPO(OH)在已报道的硼磷酸盐体系中具有最大的双折射（在546nm处Δ0.103），使KBPO(OH)成为一种有前景的深紫外双折射晶体。本研究不仅为提高硼磷酸盐的双折射提供了可行策略，还将相位匹配推进到了短波长区域。
