A₂Bi₂(SeO₃)₃F₂ (A = K and Rb): Excellent Mid-Infrared Nonlinear Optical Materials with Both Strong SHG Responses and Large Band Gaps

Abstract

A family of noncentrosymmetric alkali-metal bismuth selenite fluorides, A 2 Bi 2 (SeO 3 ) 3 F 2 [A = K(1) and Rb(2)], has been synthesized through a mild hydrothermal method. These isostructural compounds all had onedimensional [Bi 2 O 9 F 2 ] chains, which were further connected with neighbouring chains through bridged selenite groups to construct the 3D framework. Because of the relatively ordered alignment of [BiO x F y ] and SeO 3 groups, they have large second-harmonic generation (SHG) responses of about 15.0(1) and 14.4(2) times that of KH 2 PO 4 (KDP) under 1064 nm laser radiation and 0.40(1) and 0.36(2) times that of AgGaS 2 (AGS) under 2.05 μm laser radiation, respectively. In addition, the SHG response of (1) was the largest among those of all reported metal selenites. In addition, all of them had high thermal stability (∼400 °C), wide energy band gaps (over 3.72 eV), and an excellent IR transparent region, suggesting that they had great potential as high power mid-infrared nonlinear optical crystals.

Series of Luminescent Lanthanide MOFs with Regular SHG Performance

“…When a laser acts on the second-order nonlinear optical material, in addition to producing the same light (linear part) as the incident frequency w , it also generates doubled frequency light with a frequency of 2 w , called the second-harmonic generation (SHG) effect. , Being often used to represent the properties of second-order nonlinear optical materials, SHG is widely utilized in the field of harmonic imaging and sensing − for the following reasons: first, the strong localization of the nonlinear effect reduces the background interference caused by the nonfocus optics and improves the signal-to-noise ratio as well as the three-dimensional spatial resolution. At the same time, the photobleaching and phototoxicity effects on the nonfocal plane are greatly reduced, so it can image the sample for a long time without affecting its activity .…”

GaSeCl5O: A Molecular Compound with Very Strong SHG Effect

“…Thus, the combination of SeO 3 groups with [BiO x X y ] polyhedra resulted in compounds such as A 2 Bi 2 (SeO 3 ) 3 F 2 (A = K, Rb) or BaBi(SeO 3 ) 2 Cl with strong SHG effects (15 × KDP). 9,10 The introduction of SeO 3 groups is also associated with enhanced SHG effects in Bi 3 (SeO 3 ) 3 (Se 2 O 5 )F (8 × KDP) and Ba(MoO 2 F) 2 (QO 3 ) 2 (Q = Se, Te) (2−5 × KDP). 11,12 Herein, the stereochemically active lone pair of Se(IV) induces a strong polarization in the polar SeX 3 groups (X = O, Cl).…”

“…Se­(IV)-based materials show lower SHG intensities than iodates and typically outside of the visible spectrum. Thus, the combination of SeO 3 groups with [BiO x X y ] polyhedra resulted in compounds such as A 2 Bi 2 (SeO 3 ) 3 F 2 ( A = K, Rb) or BaBi­(SeO 3 ) 2 Cl with strong SHG effects (15 × KDP). , The introduction of SeO 3 groups is also associated with enhanced SHG effects in Bi 3 (SeO 3 ) 3 (Se 2 O 5 )F (8 × KDP) and Ba­(MoO 2 F) 2 ( Q O 3 ) 2 ( Q = Se, Te) (2–5 × KDP). , Herein, the stereochemically active lone pair of Se­(IV) induces a strong polarization in the polar Se X 3 groups (X = O, Cl). Partial substitution of X by other atoms in the SeO 3 group should distort the trigonal symmetry and even further enhance the polarization.…”

Sr2Nb6O13F8·4H2O and Sr3Nb2O2F12·2H2O: A Variant of Three-Dimensional Tungsten Bronze and a Polar Molecular Oxide Fluoride

“…Different types of interstitial channels also exist in which various cations with distinct size and concentration reside. On the basis of their structures, tungsten bronzes can be further classified to perovskite-type, tetragonal, hexagonal, and intergrowth tungsten bronzes. − The tungsten bronze family has also been exhibiting many fascinating characteristics including magnetic, electric, optical, and electrochromic properties. − Especially, tungsten bronzes with noncentrosymmetric (NCS) structures constructed by alignment of the distorted octahedra have revealed very interesting characteristics such as piezoelectricity, second-harmonic generation (SHG), and ferroelectricity. − The structure-related properties, mainly originating from the out-of-center distortion of second-order Jahn–Teller distortive cations, might be widely applied to operations in transducers, frequency conversions, medical lasers, optical communications, and memories. − We have been very interested in exploring tungsten bronze materials containing Nb 5+ , with the d 0 transition-metal cation exhibiting large octahedral distortion and F – being the most electronegative anion that can generate a wide transparency. , Thus far, several tungsten bronze-type niobium oxyfluorides such as NaNb 2 O 5 F, SrK 2 Nb 5 O 14 F, K 1– x Nb 3 O 9– x F x (0 ≤ x < 1), K 3 (Nb 3 Ti 2 )­O 11 F 4 , KNb 2 O 5 F, etc., have been known. In this paper, we report two new hydrothermally synthesized strontium niobium oxyfluorides, Sr 2 Nb 6 O 13 F 8 ·4H 2 O and Sr 3 Nb 2 O 2 F 12 ·2H 2 O.…”