CsHgNO₃Cl₂: A New Nitrate UV Birefringent Material Exhibiting an Optimized Layered Structure

Abstract

Developing effective strategies to design novel, excellent birefringent materials has become an emerging challenge. Herein, we report a new UV nitrate birefringent material, CsHgNO3Cl2, which is an analogue of the known UV carbonate nonlinear optical crystal KCaCO3F. In CsHgNO3Cl2, a perfect layered structure was produced owing to the alliance of a planar π-conjugated anion NO3 – and highly electropolarized Hg2+ cation. The optimized layered structure that is beneficial in enlarging the optical anisotropy induced a large birefringence (Δn = 0.145@546 nm) for CsHgNO3Cl2, even superior to that of the well-known commercial birefringent material α-BBO in the UV region. The strategy that the optimization of planar functional group arrangement is able to boost birefringence is expected to guide the development of high-performance birefringent materials in the future, especially in the field of UV.

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MIIB4O6F2 (MII=Be, Mg, Pb, Zn, Cd)

“…Borates with the planar [BO 3 ] 3− or [B 3 O 6 ] 3− groups can produce a large birefringence, [13] such as Na 3 Ba 2 (B 3 O 6 ) 2 F (Δ n =0.1020 at 1013.98 nm), [14] Ca 3 (BO 3 ) 2 (Δ n =0.0927 at 1068 nm), [15] Ba 2 Ca(B 3 O 6 ) 2 (Δ n =0.1183 at 1014 nm), [16] and Ba 2 Mg(B 3 O 6 ) 2 (Δ n =0.1081 at 1014 nm) [17] . In addition, some compounds with second‐order Jahn‐Teller effect d 0 cations, lone pair cations, or d 10 transition‐metal cations possessing polar displacements show large birefringence, [18–20] such as SbB 3 O 6 , [21] Sn 2 B 5 O 9 Cl, [22] LiHgPO 4 , [23] etc.…”

Ba2B5O8(OH)2(NO3)·3H2O: the design of an alkaline earth metal borate-nitrate optimized from a hydroxylic borate

“…27 Alternatively, introducing π conjugated anions, such as planar [CO 3 ] 2− and [NO 3 ] − units, 28 may be beneficial for enhancing the hyperpolarizability and polarizability due to the high anisotropy produced by them. [29][30][31] Moreover, the [CO 3 ] 2− and [NO 3 ] − anions are usually isolated from the borate anions, which can significantly regulate the B-O frameworks and produce novel structures. Subsequently, a series of compounds that combine borate anions and π conjugated anions have been found, such as borate-carbonates, Pb 7 O(OH) 3 (CO 3 ) 3 BO 3 and 32 boratenitrates, 33 Pb 2 (BO 3 )(NO 3 ), 34 Na 3 B 6 O 10 NO 3 35 and La[B 5 O 8 (OH)] 36 However, to the best of our knowledge, no alkaline earth metal borate-nitrate has been found by investigating the inorganic crystal structure database (ICSD-4.6.0, the latest release of ICSD-2021.1), which impels us to explore new borate-nitrates with alkaline earth metal cations.…”

The First Positive Uniaxial Cyanurate Crystals Containing a Crown-like Anionic Group Arrangement and Strengthened Optical Anisotropy

“…Thus, it still remains a great challenge to obtain an all-around birefringent crystal applied in the UV region. 21,22 Recently, the (C 3 N 3 O 3 ) 3− anion group of cyanurates, which is isoelectric with the (B 3 O 6 ) 3 23−26 Inspired by this case, the birefringence value of Ba 3 (C 3 N 3 O 3 ) 2 (BCY) (0.32 at 800 nm) is nearly 3 times higher than that of the isostructural β-BaB 2 O 4 (β-BBO) (0.119 at 546 nm). 27,28 Besides, the recently reported alkali metal/alkali earth metal (iso)cyanurates exhibit not only large birefringence but also a short UV cutoff edge (λ UV ), such as LiK(HC 3 N 3 O 3 )•2H 2 O (Δn = 0.186 at 514 nm, λ UV = 237 nm), 29 NaRb 0.86 Cs 0.14 (HC 3 N 3 O 3 )•2H 2 O (Δn = 0.238 at 532 nm, λ UV = 240 nm), 30 K 2 Ca(H 2 C 3 N 3 O 3 ) 4 •4H 2 O (Δn = 0.371 at 800 nm, λ UV = 233 nm), 31 RbNa(HC 3 N 3 O 3 )• 2H 2 O (Δn = 0.194 at 589.6 nm, λ UV = 241 nm), 32 and Ba 2 M(C 3 N 3 O 3 ) 2 (M = Mg, Ca) (Δn = 0.351, 0.345 at 800 nm, λ UV = 230 nm, 225 nm), 33 demonstrating the attractive potentials of metal cyanurates in UV birefringent applications.…”

“…Therefore, researchers attempted to design a series of borates composed of a (B 3 O 6 ) 3− unit, such as Na 3 Ba 2 (B 3 O 6 ) 2 F (0.1149 at 532 nm), Ba 2 Ca­(B 3 O 6 ) 2 (0.156 at 253.7 nm), Ba 2 Mg­(B 3 O 6 ) 2 (0.145 at 253.7 nm), and PbBa 2 (B 3 O 6 ) 2 (0.08 at 532 nm), despite that their practical application is still limited by insufficient birefringence, or narrow transmittance range. Thus, it still remains a great challenge to obtain an all-around birefringent crystal applied in the UV region. , …”