Be₂(BO₃)(IO₃): The First Anion‐mixed Van der Waals Member in the KBe₂BO₃F₂ Family with a Very Strong Second Harmonic Generation Response

Abstract

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate-iodate NLO crystal, Be 2 (BO 3 )(IO 3 ) (BBIO), by multicomponent modification of KBe 2 BO 3 F 2 (KBBF), in which the structural features of KBBF were maintained and (IO 3 ) À groups were connected to honeycomb [Be 2 BO 3 O 2 ] 1 layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO 3 ) À , (BO 3 ) 3À and (BeO 4 ) 6À groups, and exhibited a very strong SHG response of % 7.2 KH 2 PO 4 (KDP, @1064 nm) and a large birefringence (Dn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate-iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering. Creatinganewtypeofpolarornon-centrosymmetric(NCS)inorganic compounds is of great significance in the development of piezoelectric, pyroelectric, ferroelectric, and especially nonlinear optical (NLO) materials. Although significant efforts have been devoted to looking for new NLO crystals from various types of compounds, such as borates, carbonates, iodates, phosphates, sulfates, etc., [1] it is still very challenging to rationally design and synthesize polar or NCS crystals with large second harmonic generation (SHG) effects, sufficient birefringence, and wide band gaps from these traditional compound systems. Recently, mixing two types of NLO-active anionic groups in the same crystal has been proved as a convenient molecular design strategy for designing new NLO materials. Besides, it is possible to precisely tailor the physical and chemical properties of crystalline materials by hybridizing anionic groups with different properties. This strategy afforded several excellent NLO compounds with mixed anionic groups, such as Bi 3 TeBO 9 , [2] B 2 S 2 O 9 , [3] Pb 2 (BO 3 )(NO 3 ), [4] Ba 3 (ZnB 5 O 10 )PO 4 , [5] Nb 2 O 3 (IO 3 ) 2 (SO 4 ), [6] Sc(IO 3 ) 2 (NO 3 ). [7] However, borate-iodate mixed NLO materials have never been reported due to the difficulty in synthesis, though the combination of diverse B-O groups and (IO 3 ) À group with super large, microscopic second-order NLO susceptibility may lead to novel NLO crystals with excellent optical properties. Herein, the first borate-iodate NLO crystal will be reported.According to our previous report of the two centrosymmetric metal borate-iodates, Sr[B(OH) 4 ](IO 3 ) and Li 4 Sr 5 [B 12 O 22 (OH) 4 ](IO 3 ) 2 , [8] in which the B-O and (IO 3 ) À groups were isolated from each other and formed pseudotwo-dimensional (2D) layered structures with borate and iodate layers stacked alternately, a new synthesis strategy has been designed in this study. To obtain NCS borate-iodates, it may be better to construct a stable polar borate layer first as a polar structure inducer. Therefore, the most famous deepultraviolet (deep-UV) NLO crystal KBBF with honeycomb 2D [Be 2 BO 3 F 2 ] 1 layers was chosen...

AZn2(BO3)Si2O5 (A = Rb, Cs): first examples of KBe2BO3F2 structure type in the borosilicate family exhibiting a deep-ultraviolet cutoff edge

“…21–28 Anionic group combinations not only initiate structural diversities, but also modulate the physio-chemical properties of the NLO crystals. Within the mixed anions based NLO crystal classes, inorganic borate derivatives were enthusiastically explored, by involving boron-based anionic units into other systems, a new set of NLO materials classes can be obtained, such as borophosphates, 29,30 borogermanates, 31 borosilicates, 32,33 borosulfates, 34,35 borate–iodates, 36,37 and so on. Among the above classes, borophosphates captured relatively early attention, and some promising results were achieved.…”

“…Recent success in the KBBF template-based group UV NLO crystal design is well manifested in fluorooxoborates, 43,44 among which NH 4 B 4 O 6 F, 45 CsB 4 O 6 F, 46 are highly regarded as plausible alternatives to KBBF. To date, several KBBF type inorganic borate derivatives, as well as mixed anionic group NLO crystals with an impressive optical performance, have been discovered, such as Pb 2 BO 3 I, 36 Be 2 (BO 3 )(IO 3 ), 37 AZn 2 BO 3 X 2 (A = K, Rb, NH 4 ; X = Cl, Br), 47 K 2 Sb(P 2 O 7 )F, 48 NaZnCO 3 (OH), 49 C(NH 2 ) 3 SO 3 F 50 and so forth. Recently, the KBBF type birefringent crystal Sn 2 PO 4 I, 51 with an outstandingly large birefringence (0.466 at 1064 nm) was also designed.…”

Unprecedented boat-shaped [Mo2O5(IO3)4]2− polyanions induced a strong second harmonic generation response

“…); 23–25 (d) the condensation of IO x ( x = 3 and 4) into polyiodates. 26 As a result, many excellent SHG iodates with extremely strong SHG response and wide optical transparency window were successfully designed and synthesized, such as Li 2 Ti(IO 3 ) 6 (500 × α-SiO 2 ), 27 K(VO) 2 O 2 (IO 3 ) 3 (3.6 × KTP), 28 BiOIO 3 (12.5 × KDP), 29 PbPt(IO 3 ) 6 (H 2 O) (8 × KDP), 30 Be 2 (BO 3 )(IO 3 ) (7.2 × KDP), 31 Sc(IO 3 ) 2 (NO 3 ) (4 × KDP), 32 NaI 3 O 8 (300 × α-SiO 2 ) 33 and YI 5 O 14 (14 × KDP). 34…”

A Lead Mixed Halide with Three Different Coordinated Anions and Strong Second‐Harmonic Generation Response

“…However, it is difficult to balance these NLO performances, like SHG intensity and LDT, in a crystal with only one type anion [18] . Inspired by KBBF, many NLO materials have been reported in recent years by the combination of two types of anions or anionic groups, including hydroxycarbonate, fluorinated sulfate, fluorotellurite, borate halides, borate hydroxides, iodate halides, iodate‐nitrate, carbonate halides, phosphate halides, selenite halides, nitrate hydroxides, and so on [18–25] …”