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Efficient resonant electron transfer from the surface bonding structure to the conduction band of quantum confined Si nanocrystals is observed by Si nanocrystals in a toluene suspension. Based on the electron transfer mechanism, the enhancement of photoluminescence originates from the band-to-band recombination in the p-type Si nanocrystals suspended in a toluene solution. The energy levels of the electrons in the Si nanocrystals chemisorbed with toluene molecules are calculated using the method of linear combination of atomic orbitals, and the characteristics of the obtained density of states is in good agreement with the observed photoluminescence properties. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) measurements have been performed on the nanocomposites of higher fullerene-coupled porous silicon (PS) nanocrystals. For the C70/PS and C76(78)/PS nanocomposites, the PL spectra show a pinning wavelength at ∼565 nm and for the C84/PS and C94/PS nanosystems the pinning wavelength is at ∼590 nm. The PL pinning property is closely related to the sorts of the coupled fullerenes. A band mixing model of direct and indirect gaps in a nanometer environment consisting of nc-Si core, SiO2 surface layer, and coupled fullerene has been proposed for calculation of electronic states. Good agreement is achieved between the experiments and theory. [ABSTRACT FROM AUTHOR]

Using an anodic alumina membrane with an ordered nanopore array as a template, we have fabricated a two-dimensional light-emitting nanopolymer array by embedding the luminescence polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) into the nanopores. It is revealed experimentally that the conformation of the MEH-PPV chains in the nanopores is in the form of a bunch of polymer chains. The number of the polymer chains in a bunch depends on the concentration of the polymer solution and the diameters of nanopores in the template. Investigation on the photoluminescence spectra of the nano-MEH-PPV array annealed under different temperatures shows that the nanopores can effectively hinder the relaxation of MEH-PPV, which leads to its high thermal stability. [ABSTRACT FROM AUTHOR]

Using the bandmixing model of direct and indirect gaps, we calculate the energy levels of electrons and holes confined in the Si/FeSi2 nanocomposite consisting of nanocrystalline Si core, interfacial FeSi2 layer, and outer Fe2O3 crust. The obtained results explain very well the intensity enhancement and pinning behavior of the observed photoluminescence peaks after the nanocomposite is stored in air. We also theoretically obtain the photoluminescence excitation characteristics. Good agreement is achieved between the theory and experiments. [ABSTRACT FROM AUTHOR]

We have investigated the role of the solvents in the luminescence from colloidal 3C-SiC suspensions. By dispersing electrochemically etched polycrystalline 3C-SiC wafers in water, ethanol, or toluene, we have fabricated suspensions of 3C-SiC nanocrystals that exhibit intense photoluminescence. By taking into account the quantum confinement effect and observed size distributions of the 3C-SiC crystallites, a simple model is formulated to explain the photoluminescence spectra. Our results show that the colloidal 3C-SiC nanocrystals are robust and intense emitters that have good chemical stability and biocompatibility. They are thus useful in biotechnology and nano-optoelectronics applications. [ABSTRACT FROM AUTHOR]

We report on cathodoluminescence (CL) of monosized and well-aligned 4 Å single-walled carbon nanotubes in a zeolite template (AlPO4-5 single crystal). The CL exhibits three emission bands centered at 1.87, 2.22, and 2.98 eV, which are assigned to three possible 4 Å tube structures (4,2), (5,0), and (3,3), respectively. The assignation is based on first-principles calculations, Raman scattering measurement, and CL behavior of various samples. The emission peak shift of the (5, 0) tube is explained by the transition mechanism being different from photoluminescence due to the excitation of electrons with high energy. [ABSTRACT FROM AUTHOR]