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Full and shortened single-walled and multiple-walled carbon nanotubes were suspended in water to form stable suspensions in the presence of a surfactant. Optical limiting properties of the suspensions were determined for 532-nm pulsed laser irradiation, and the results were comparable with those of carbon black aqueous suspension. Solubilization of the shortened carbon nanotubes was achieved by attaching the nanotubes to highly soluble poly(propionylethylenimine-co-ethylenimine) or by functionalizing the nanotubes with octadecylamine. The soluble carbon nanotube samples formed homogeneous solutions in room-temperature chloroform. Optical limiting properties of these solutions were also determined for 532-nm pulsed laser irradiation, and the results were found to be quite different from those of the carbon nanotube aqueous suspensions. Apparently, the carbon nanotubes exhibit significantly weaker optical limiting responses in homogeneous solutions than in suspensions. Mechanistic implications of the experimental results are discussed.

Metal and metal sulfide nanoparticles are prepared using a method that is based on the rapid expansion of supercritical fluid solution (RESS) into a liquid solution and characterized using transmission electron microscopy and X-ray diffraction methods. The nanoparticles form solution-like stable suspensions in the presence of a stabilization agent such as poly(N-vinyl-2-pyrrolidone) (PVP) polymer. The stable suspensions allow systematic nonlinear optical measurements. The nanocrystalline silver metal and silver sulfide particles in PVP polymer-stabilized ethanol suspensions of high linear transmittance exhibit excellent optical limiting properties, with the optical limiting responses toward nanosecond laser pulses at 532 nm being much stronger than those of benchmark materials [60]fullerene and chloroaluminum phthalocyanine in solution. A comparison of the results with those of stable suspensions of other nanoparticles including cadmium sulfide, lead sulfide, and nickel suggests that the optical limiting properties are unique to the nanoscopic silver-containing materials. Mechanistic issues concerning the optical limiting performance of the silver-containing nanocrystalline particles are discussed, and a nonlinear absorption mechanism is proposed.

Strong luminescence emissions over a broad wavelength region were detected from well-dispersed carbon nanotubes in most functionalized samples, even with excitation wavelengths into the near-IR. Apparently, the better dispersion and functionalization of the nanotubes resulted in more intense luminescence emissions. These emissions may logically be attributed to the trapping of excitation energy by defect sites in the nanotube structure, which are passivated upon the appropriate functionalization of the nanotubes. Better functionalization improves not only the nanotube dispersion (thus diminishing the quenching due to intertube interactions) but also the surface passivation to make the energy trapping sites more emissive, leading to stronger luminescence emissions. Because of such high sensitivity, the visible luminescence emissions may prove valuable in the evaluation of dispersion in functionalized carbon nanotube samples and related nanocomposite materials.