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Nonlinear Active Materials: An Illustration of Controllable Phase Matchability

Lu, Hongcheng, Gautier, Romain, Donakowski, Martin D., Tran, T.Thao, Edwards, Bryce W., Nino, Juan C., Halasyamani, P. Shiv, Liu, Zhengtang, Poeppelmeier, Kenneth R.
Journal of the American Chemical Society 2013 v.135 no.32 pp. 11942-11950
crystallization, crystals
For a crystal to exhibit nonlinear optical (NLO) activity such as second-harmonic generation (SHG), it must belong to a noncentrosymmetric (NCS) space group. Moreover, for these nonlinear optical (NLO) materials to be suitable for practical uses, the synthesized crystals should be phase-matchable (PM). Previous synthetic research into SHG-active crystals has centered on (i) how to create NCS compounds and/or (ii) how to obtain NCS compounds with high SHG efficiencies. With these tactics, one can synthesize a material with a high SHG efficiency, but the material could be unusable if the material was nonphase-matchable (non-PM). To probe the origin of phase matchability of NCS structures, we present two new chemically similar hybrid compounds within one composition space: (I) [Hdpa]₂NbOF₅·2H₂O and (II) HdpaNbOF₄ (dpa = 2,2′-dipyridylamine). Both compounds are NCS and chemically similar, but (I) is non-PM while (II) is PM. Our results indicateconsistent with organic crystallographythe arrangement of the organic molecule within hybrid materials dictates whether the material is PM or non-PM.