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Published on: July 18, 2015
Designing Novel Solar-Blind Ultraviolet Nonlinear Optical Crystals Based on Local Proton Distribution Complementary
Hongyuan Sha1, Dongling Yang1,2, Lilin Yang3
1Research Center for Crystal Materials, CAS Key Laboratory of Functional Materials and Devices for Special Environmental Conditions, Xinjiang Key Laboratory of Functional Crystal Materials, Xinjiang Engineering Technology Research Center for Optoelectronic Crystals and Devices, Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, Urumqi, China.
Abstract:
Dipolar π-conjugated groups with large polarizability anisotropy and hyperpolarizability are generally regarded as important nonlinear optical (NLO) active building units. However, their strong dipole-dipole interactions remain a key challenge in designing non-centrosymmetric structures. To overcome this, we proposed a novel non-centrosymmetric structure design strategy based on the local proton distribution complementary effect. Importantly, it could induce the groups to form a zigzag ordered arrangement along the direction perpendicular to the π-conjugated plane, thereby significantly increasing the probability of forming non-centrosymmetric structures. Based on this strategy, we successfully designed and synthesized two novel solar-blind ultraviolet non-centrosymmetric crystals, (C3N2H5)Na3(S2O3)2·2H2O and (C3N2H5)ClO4·(C3N2H4), with imidazolium/imidazole groups. Both crystals exhibit excellent optical performances, with a large birefringence of 0.158 @ 546 nm in (C3N2H5)ClO4·(C3N2H4) and a strong NLO effect approximately 2.6 times that of KH2PO4 in (C3N2H5)Na3(S2O3)2·2H2O, which mainly result from the intrinsic characteristics of imidazolium/imidazole groups and their ordered arrangement. Consequently, this work not only develops two promising solar-blind UV NLO crystals but also offers a novel structure design strategy that is expected to promote the development of NLO materials.

