LiB5O5F2(OH)4: A new deep-ultraviolet birefringent crystal with [B5O5F2(OH)4] anionic group

Performance of optical materials with the derivative of planar π-conjugated groups: Recent advances and future prospects

“…LiB 5 O 5 F 2 (OH) 4 was synthesized through the solid-state method and belongs to the space group P 2 1 / m of the monoclinic system. 70 As shown in Fig. 7, the B atoms link with O/F atoms to exhibit three coordination patterns, namely the [BO 3 ], [BO(OH) 2 ] and [BO 2 F 2 ] units, which further connect with each other by sharing bridge O atoms to form the [B 5 O 5 F 2 (OH) 4 ] FBUs.…”

CsB3O4(OH)2: a new deep-ultraviolet birefringent crystal with [B3O4(OH)2] anionic group

“…According to previous research, the introduction of OH can eliminate the dangling bond of the terminal O atom, thereby increasing the band gaps. 6–8,21,23–26 It can also effectively increase the anisotropic polarization of [BO 3 ] units, leading to the delocation of π-electrons. For example, LiB 5 O 5 F 2 (OH) 4 , 6 Na[B 3 O 3 F 2 (OH) 2 ]·[B(OH) 3 ], 8 NH 4 B 11 O 16 (OH) 2 , 7 CaBO 3 H, 27 and NH 4 (B 6 PO 10 (OH) 4 )·H 2 O, 28 have been reported showing large birefringence.…”

“…6–8,21,23–26 It can also effectively increase the anisotropic polarization of [BO 3 ] units, leading to the delocation of π-electrons. For example, LiB 5 O 5 F 2 (OH) 4 , 6 Na[B 3 O 3 F 2 (OH) 2 ]·[B(OH) 3 ], 8 NH 4 B 11 O 16 (OH) 2 , 7 CaBO 3 H, 27 and NH 4 (B 6 PO 10 (OH) 4 )·H 2 O, 28 have been reported showing large birefringence. In addition, the coordinated hydroxyl groups can bring new forms of hydrogen bonds, which is conducive to crystal growth under hydrothermal conditions.…”

“…As the demand for high-performance birefringent materials increases, a series of related designs and explorations have been undertaken. [6][7][8][9] For example, Cs 2 Bi 2 OSi 2 O 7 , 10 CeF 2 (SO 4 ), 11 Rr[B(OH) 4 ](IO 3 ), 12 MLAPbBr 4 (MLA = melamine), 13 and Rb 2 VO (O 2 ) 2 F 14 have been reported with large birefringence. However, the biggest challenge is to maintain a balance between the large birefringence and band gaps.…”

“…Moreover, [BO 3−n (OH) n ](n = 1,2,3) units inherently possess large anisotropic polarizability and highest unoccupied molecular orbital-lowest unoccupied molecular orbital (HUMO-LUMO) gap energy. 6 At the same time, previous studies have shown that the synergistic effect of π-conjugate units and non-π-conjugated units is used to enhance optical anisotropy. 8 Based on this, the introduction of heteroanions (e.g., [BO 3 OH], [BO 3 F], [BO 2 F 2 ]) into borates along with π-conjugated anion units is expected to be a promising way for designing new DUV birefringent crystals.…”