The role of cations in second-order nonlinear optical materials based on π-conjugated [BO 3 ] 3− groups

By Yaoguo Shen, Sangen Zhao, Junhua Luo. Coordination chemistry reviews, 2018

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Abstract Nonlinear optical (NLO) materials play a significant role in laser science and technology as they can efficiently expand the fixed (or limited) wavelengths of common laser sources. π-Conjugated [BO3]3− groups are widely accepted to be one of the most desirable structural groups of NLO materials. A number of NLO materials are composed of [BO3]3− groups and some of them have been commercially produced and used. The anionic group theory tells researchers what kind of arrangement for anionic groups is beneficial to generate large second-order NLO responses; nevertheless, it does not answer the key question that how to realize the desirable arrangement of anionic groups. Here we systematically review NLO materials with [BO3]3− groups to provide a deep understanding on the underlying structure-properties relationship between the microscopic electronic configuration of π-conjugated [BO3]3− groups and macroscopic optical properties of NLO materials. More importantly, some findings can be concluded. Firstly, the cationic MOxFy (x = 3, 4, 5, 6, 8; y = 0, 1, 2) polyhedron with three equatorial oxygen atoms are prone to make the [BO3]3− groups in coplanar and aligned arrangement around the base of a polyhedron, which is beneficial to generate sufficiently large second-harmonic generation and moderate birefringence (or good phase-matchability). Secondly, in some cases the secondary cations (ions with less electronegativy) in one compound have an additional effect on the overall arrangement of [BO3]3− groups. This work would shed useful insights on how to rationally design and synthesize new superior NLO materials with [BO3]3− groups.

Subfields: Electronic, Optical and Magnetic Materials, Geophysics, Materials Chemistry

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