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Published on: October 31, 2019
Local Conformational Confinement and Dipole Engineering for Phase-Matchable Solar-Blind Ultraviolet Nonlinear Optical
Guangsheng Xu1,2, Junwei Feng1, Luyong Zhang1,2
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 Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011, China.
None:
Solar-blind ultraviolet nonlinear optical crystals are difficult to design because efficient frequency conversion requires the simultaneous realization of noncentrosymmetry, phase-matchable birefringence, and a sufficiently wide band gap. Here, we introduce a local conformational-confinement strategy that transforms flexible malonate into chelated [C3H2O4BFR]- (R = F, Me, CF3) chromophores, in which a six-membered ring fixes the relative orientation of two carboxylate π-conjugated units. This geometric locking enhances polarizability anisotropy and microscopic hyperpolarizability without sacrificing the band gap. In parallel, substitution at the boron-bound R site tunes the ground-state dipole moment of the anionic functional unit, suppressing antiparallel dipole packing and promoting noncentrosymmetric crystallization. Guided by this dual design principle, we obtained NaMaBFMe, which combines a UV cutoff edge near 220 nm, birefringence of 0.131 at 1064 nm, a phase-matchable SHG response of 2.4 × KDP, and a laser-induced damage threshold of 1.258 GW·cm-2. These results establish conformational locking coupled with dipole engineering as a general route to high-performance solar-blind UV NLO crystals.
