Giant Optical Anisotropy in the UV‐Transparent 2D Nonlinear Optical Material Sc(IO₃)₂(NO₃)

Abstract

Birefringence is a fundamental optical property for linear and nonlinear optical (NLO) materials. Thus far, it has proved to be very difficult to engineer large birefringence in optical crystals functioning in the UV region. Herein, we report the first 2D rare‐earth iodate–nitrate crystal Sc(IO3)2(NO3) (SINO), which is shown to exhibit giant optical anisotropy. Air‐stable SINO possesses a short UV absorption edge (298 nm), a strong NLO response (4.0 times that of benchmark KH2PO4) for the nitrate family, and the largest birefringence (Δn=0.348 at 546 nm) of inorganic oxide optical crystals. The unusually large birefringence and NLO response can be attributed to an optimized 2D layered structure, combined with highly polarizable and anisotropic building units [IO3]− and [NO3]−. These findings will facilitate the development of UV linear and NLO materials with giant optical anisotropy and promote their potential application in optoelectronic devices.

AX·(H2SeO3)n (A = K, Cs; X = Cl, Br; n = 1, 2): A Series of Ionic Cocrystals as Promising UV Birefringent Materials with Large Birefringence and Wide Band Gap

“…To search for new birefringent materials, it is necessary to introduce birefringence-active units with larger optical anisotropy. , Stereochemical active lone pair (SCALP) cations (Pb 2+ , Se 4+ , Bi 3+ , Sb 3+ , Sn 2+ , etc. ) − can form distorted polyhedra with large optical anisotropy because the presence of lone pairs can impose the repulsive interaction with anions, so the SCALP cations are considered to be one type of attractive birefringence-active units. − Benefiting from the distorted polyhedra with SCALP cations, compounds like Sn 2 B 5 O 9 Cl (0.171 at 546 nm), SbB 3 O 6 (0.318 at 546 nm), α-SnF 2 (0.191 at 546 nm), LiGaF 2 (IO 3 ) 2 (0.206 at 532 nm), SrZnSnSe 4 (0.29 at 1240 nm), Cd 2 Nb 2 Te 4 O 15 (0.13 at 546 nm), K 2 Sb­(P 2 O 7 )F (0.162 at 546 nm), and Rb 2 Sn 2 F 5 Cl (0.31 at 532 nm) have remarkable birefringence.…”

Colossal Optical Anisotropy from Atomic‐Scale Modulations

“…Birefringence is the dependence of the refractive index on the polarization of light travelling through a material and is of paramount importance for applications from classical to quantum optics. [1][2][3][4][5][6][7][8][9][10][11] The observation of birefringence in calcite as early as 1669 [12] -called Iceland spar at the time-eventually led to Fresnel's insight in 1821 that light is a transverse wave. [13,14] Calcite's record as the most birefringent material stood for over a century, with Δn = |n e − n o | = 0.17 in the visible, as analyzed and explained by Bragg; [15] here, n e and n o are respectively the extraordinary and ordinary refractive index.…”

(C(NH2)3)2(I2O5F)(IO3)(H2O) and C(NH2)3IO2F2: Two Guanidine Fluorooxoiodates with Wide Band Gap and Large Birefringence

“…The birefringence of a material is often closely related to the polarization anisotropy, which is determined by the arrangement of its functional groups. In general, non-π-conjugated units, such as [BO 4 ] and [PO 4 ] units, have a large HOMO–LUMO band gap, which is conducive to the blue shift of the cutoff edge, but their low polarization anisotropy leads to small birefringence. , According to the fluorine substitution strategy, partial oxygen atoms in [BO 4 ] and [PO 4 ] are replaced by F, resulting in [MO x F 4– x ] ( x +1)– (M = B, x = 1, 2, 3; M = P, x = 2, 3) groups, which can provide a good balance between birefringence and band gap, − such as AB 4 O 6 F (A = NH 4 , Na, Rb, Cs), MB 5 O 7 F 3 (M = Mg, Ca, Sr, Pb), (NH 4 ) 2 PO 3 F, and so on. − In contrast, π-conjugated elements such as [BO 2 ], [MO 3 ] (M = B, C, N), and [H x C 3 N 3 O 3 ] ( x = 0, 1, 2, 3) with triangular or planar structures are conducive to the enhancement of birefringence. − In addition, the lone pair electron of I 5+ in iodates has stereochemical activity, which is conducive to the generation of greater birefringence. − Recently, the introduction of fluorine atoms into iodates has become an increasingly hot research topic because the negative effect of lone pair electrons on the UV cutoff edge can be compensated. Meanwhile, more abundant and diverse structures can be obtained.…”