The first metal iodate fluoride, Bi(IO )F , with a strong second harmonic generation (SHG) effect has been prepared. Bi(IO )F crystallizes in the polar space group C2 and features a three-dimensional [BiF ] cationic framework with IO groups capping the inner walls of the one-dimensional tunnels. This [BiF ] cationic framework acts as a template for the assembly of the polar IO units in a favorable superposed fashion, which leads to the polar structure of the material. Bi(IO )F displays a rather wide transmittance window (0.3-11 μm) and exhibits a very strong SHG response that is about 11.5 times larger than that of KH PO (KDP) under 1064 nm laser radiation and the same as that of KTiOPO (KTP) under 2.05 μm laser radiation. Preliminary investigations indicate that Bi(IO )F is a promising nonlinear optical material in the visible and mid-IR region.

A new ultraviolet nonlinear optical material, namely LiHgPO4, was synthesized using the mild hydrothermal method. The structure of LiHgPO4 features novel double layers constructed by severely distorted HgO6 octahedra and PO4 tetrahedra, which are further interconnected by LiO4 tetrahedra to form a three-dimensional structure. LiHgPO4 exhibits a very strong second harmonic generation (SHG) response of 11.0 times that of KH2PO4 and a relatively large birefringence (0.068 at 1064 nm) among the reported SHG-active phosphates. Theoretical calculations revealed that the introduction of the Hg2+ in a highly distorted HgO6 octahedral geometry is crucial to produce the strong SHG response and large birefringence.

Tw om ixed-metal gallium iodate fluorides,n amely, a-and b-Ba 2 [GaF 4 (IO 3 ) 2 ](IO 3 )(1 and 2), have been designed by the aliovalent substitutions of a-a nd b-Ba 2 [VO 2 F 2 (IO 3 ) 2 ]-(IO 3 )( 3 and 4)i nvolving one cationic and two anionic sites. Both 1 and 2 display large second-harmonic generation responses ( % 6 KH 2 PO 4 (KDP)), large energy band gaps (4.61 and 4.35 eV), wide transmittance ranges ( % 0.27-12.5 mm), and high relevant laser-induced damage thresholds (29.7 and 28.3 AgGaS 2 ,r espectively), whichi ndicates that 1 and 2 are potential second-order nonlinear optical materials in the ultraviolet to mid-infrared. Our studies propose that three-site aliovalent substitution is af acile route for the discovery of good NLO materials.Noncentrosymmetric (NCS) oxide materials have extensively excited academic interest owing to their probable properties with applications in second-order nonlinear optics (NLO) as well as in pyroelectrics,f erroelectrics,a nd piezoelectrics. [1][2][3][4][5][6] To the best of our knowledge,a ne xcellent second-order NLO material should feature al arge second harmonic generation (SHG) coefficient, ahigh relevant laserinduced damage threshold (LDT), appropriate optical transmittance range,m oderate birefringence for achieving phase matching,and good thermal stability.Inaddition, it should be free of moisture and accessible by af acile synthetic method. [7][8][9] Metal iodates currently attract extensive research interest due to their potential outstanding SHG response. [10] Up to now,several effective synthetic routes have been reported for exploring the NCS metal iodates featuring novel crystal structures and remarkable SHG performance,s uch as condensing IO 3 À and IO 4 3À units to form polyiodates, [11][12][13] combining six-or five-coordinate d 0 transition metal (TM) cations (e.g.T i 4+ ,V 5+ ,M o 6+ ,a nd Nb 5+ ) [14][15][16][17][18][19][20][21][22] or metal cations (e.g. Bi 3+ and Pb 2+ ) [23][24][25][26] having as tereochemically active lone-pair (SCALP) with iodates,a nd introducing fluoride anions into iodates. [27][28][29][30][31][32] Anumber of excellent SHG materials have been discovered, for instance,NaI 3 O 8 , [11] Cs 2 I 4 O 11 , [13] Li 2 M(IO 3 ) 6 (M = Ti 4+ ,Sn 4+ ,Ge 4+ ), [33][34][35] A(VO) 2 O 2 (IO 3 ) 3 (A = K, Rb,C s, NH 4 ), [15,20] AMoO 3 IO 3 (A = Rb,C s), [14] BaNbO-(IO 3 ) 5 , [17] BiOIO 3 , [23] PbPt(IO 3 ) 6 , [25] Bi(IO 3 )F 2 , [28] and KBi 2 -(IO 3 ) 2 F 5 , [30] which can produce very strong SHG effects (> 10 KH 2 PO 4 (KDP)).Recently,anumber of new NCS crystals were obtained by the aliovalent substitution of known parent compounds to produce materials with strong SHG response. [36][37][38][39][40][41] For example,S e IV O 3 2À has typically been used as as urrogate for I V O 3 À ,w ith substitution of the oxo anion by ah alide anion (usually fluoride anion) to maintain charge balance.T he first bismuth selenite fluoride,B iFSeO 3 ,w ith the strongest SHG performance of all metal selenites,was designed by aliovalent substitution of laye...