LiB_(5)O_(5)F_(2)(OH)_(4):A new deep-ultraviolet birefringent crystal with[B_(5)O_(5)F_(2)(OH)_(4)]anionic group

A new deep-ultraviolet(DUV)birefringent crystal,LiB_(5)O_(5)F_(2)(OH)_(4)(LBOFH),was designed and synthesized by a high-temperature solution method.Its structure features a[B_(5)O_(5)F_(2)(OH)_(4)]anionic group that is constructed by four π-conjugated units,i.e.,two[BO_(3)]units and two[BO(OH)_(2)]units connected by the[BO_(2)F_(2)]unit,which forms a near-coplanar configuration.The group exhibits large anisotropic polarizability and highest unoccupied molecular orbital-lowest unoccupied molecular orbital(HUMO-LUMO)gap,thus providing a good balance between the large birefringence(0.124 at 546 nm)and band gap(7.99 eV)in LBOFH.This work suggests new possibilities for the design and fabrication of advanced DUV birefringent crystals using the novel anionic group and the expansion of their alternative system with new hydroxyfluorooxoborates.

Compounds consisting of coplanar π-conjugated B_(3)O_(6)-typed structures:An emerging source of ultraviolet nonlinear optical materials

Nonlinear optical(NLO)materials as a crucial part of the laser science have attracted increasing attention from researchers because of their wide applications in information storages,modern science and technologies,et al.Based on the anionic group theory,theπ-conjugated 6-membered rings(6-MRs),B_(3)O_(6)-typed structures have key contributions to the superior optical properties ofβ-Ba_(2)B_(2)O_(4)(β-BBO).In recent years,the organic coplanarπ-conjugated B_(3)O_(6)-typed structures have caught researchers'attention due to similar configurations to the(B_(3)O_(6))groups,which are the potential sources for expending the(B_(3)O_(6))groups with outstanding optical properties.Up to know,researchers have obtained many ultraviolet(UV)NLO crystals with excellent properties withπ-conju-gated B_(3)O_(6)-typed groups.Herein,these B_(3)O_(6)-typed groups could be divided into different categories according to the atoms constituting the 6-MRs:(H_(x)C_(3)N_(3)O_(3))^(x-3)(x=0-3)(cyanurate ion),(H_(x)C_(4)N_(2)O_(3))^(x-4)(x=2,3)(barbi-turate ion),(C_(3)H_(7)N_(6))^(+)(melamine ion),(C_(5)H_(6)ON)^(+)(4-hydroxypyridine cation),and(C_(4)H_(6)N_(3))^(+)(2-amino-pyrimidinium cation).In this review,we introduced the research advances of NLO materials withπ-conjugated B_(3)O_(6)-typed groups,and summarized the crystal structures,synthetic methods,optical performances,as well as the relationships between structures and properties.This work provided a clear perspective for understanding the coplanarπ-conjugated B_(3)O_(6)-typed groups with their optical functional properties and promote the searches to develop potential NLO functional crystals.