Optical Properties in Nanofluids of Gold Nanoparticles in Poly(vinylpyrrolidone)
Nanofluids of selective visible colors are developed in gold nanoparticles embedded in polymer molecules of polyvinyl pyrrolidone (PVP) in water. A simple HAuCl4 reaction with PVP molecules (a weak reductant) in aqueous solution at 60–70 °C yields the nanofluid in a single process step with an Au3+ → Au caloric reduction. Part of PVP molecules, which binds to a resulting Au-nanoparticle of nascent surfaces, insulates it from the Au3+ species and thus disrupts it to grow further, by immobilizing in the PVP molecules. Varying the 0–1.0 wt% Au-contents (in Au-PVP) tunes effectively the Au-surface plasmon bands (SPR) in Au-core–shell particles in conjunction with the surface PVP molecules. Characteristic SPR absorption band shifts regularly from at 535 nm in 0.05 wt% Au to a value as large as 571 nm upon increasing the Au-content to 1.0 wt%. The SPR band favors emission at ∼440 nm in a core → shell energy transfer in core–shell particles of an exchange coupled system, when irradiating at ∼250 nm in the 5d106s → 5d96sp (Au) interband transition. Electron microscopic images, with the electron diffraction, reveal small Au-crystallites in shapes of cuboids (or bars) of core–shells, with 5–10 nm width (5–15 length), and their clusters of mostly pentagons.
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Document Type: Research Article
Publication date: 2009-07-01
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