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Notable Third-Order Optical Nonlinearities Realized in Layer-by-Layer Assembled Composite Films by Intercalation of Porphyrin/Polyoxometalate into Layered Double Hydroxide

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posted on 21.09.2016, 22:43 authored by Guanying Zhu, Yi Long, Haizhou Ren, Yunshan Zhou, Lijuan Zhang, Zonghai Shi, Farooq K. Shehzad, Hafiz Muhammad Asif
A series of uniform and smooth (TCPP/LDH)n films and (TCPP/P5W30/LDH)n films were fabricated with meso-tetrakis­(p-carboxyphenyl)­porphyrin (TCPP), Preyssler-type polyoxometalate K12.5Na1.5[NaP5W30O110]·15H2O (P5W30), and exfoliated Mg2Al–NO3 layered double hydroxide (LDH) monolayer nanaosheets by layer-by-layer assembly technique. The resulting films were characterized by UV–visible spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and fluorescence spectroscopy. Their third-order nonlinear optical properties were studied by Z-scan measurement with laser pulse duration of 6–7 ns at a wavelength of 532 nm. The (TCPP/LDH)n films exhibit notable self-defocusing effect and saturated absorption effect which is different from TCPP solution. The optical nonlinearity of films becomes larger with the increase of the number of bilayers. The third-order nonlinear optical coefficient χ(3) of (LDH/TCPP)50/LDH is calculated to be (6.4 ± 0.18) × 10–11 esu. Remarkably, experimental results showed that the (LDH/P5W30/LDH/TCPP)n/LDH films exhibit much larger nonlinearity than that of the (LDH/TCPP)n/LDH films when n is the same, which is thought to result from the interlayered charge/energy transfer between porphyrin and polyoxometalate although the LDH sheet is electron-inert material.

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