Nanocomposites consisting of PbS nanocrystals in a conjugated polymer matrix were fabricated. We report results of photo-and electroluminescence across the range of 1000 to 1600 nm with tunability obtained via the quantum-size effect. The intensity of electroluminescence reached values corresponding to an internal quantum efficiency up to 1.2%. We discuss the impact of using different-length capping ligands on the transfer of excitations from polymer matrix to nanocrystals.

We report on two different crystalline phases of tris͑8-hydroxyquinoline͒ aluminum (Alq 3) which were obtained by thermal sublimation in a horizontal glass tube. These phases are investigated by x-ray powder diffraction, Raman and infrared spectroscopy, and low temperature photoluminescence measurements. Apart from the already known ␣ phase we could identify a new crystalline phase of Alq 3 (␦-Alq 3) showing blueshifted fluorescence. As compared to the ␣ phase this new phase is characterized by a larger unit cell volume, a reduced number of Raman lines in the energy range between 70 and 700 cm Ϫ1 , a blueshift of the photoluminescence maximum by about 0.2 eV, and a decreased intersystem crossing to the triplet state. These differences are interpreted in terms of the isomery of the Alq 3 molecule. It is supposed that the new phase contains the facial isomer, whereas in the other phases only the meridianal isomer was reported. Low temperature photoluminescence spectra show a well-resolved vibronic progression with about the same spacing of 550 cm Ϫ1 for both crystalline phases of Alq 3. Site-selective photoluminescence measurements reveal the existence of an additional redshifted featureless emission, which is ascribed to energy relaxation into low-lying states.

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A uniform array of a new type of heterojunction formed between carbon nanotubes and silicon is studied. The heterojunction array was controllably grown with parallel and uniform nanotubes vertically aligned to the silicon substrate using a self-organized nanopore array template. The pronounced rectifying characteristics of the heterojunction were measured with an on/off ratio as high as 10(5) at 4 V. The analysis shows a large and type-I band offset at the heterojunction. The charge transport in the nanotubes is found to be strongly coupled to and limited by the dielectric charging and polarization in the hosting alumina matrix surrounding the nanotubes.

We study and demonstrate a periodic array of "carbon nanotube-silicon" heterojunctions, its functioning as an infrared (IR) detector, and report on the first observation of near-to mid-IR photocurrent response in both the cooled and uncooled modes. The formation of carbon nanotubes in a periodic dense array, parallel to each other and perpendicular to the silicon substrate, offers a new promising IR material platform with spectral tunability and scalability in field size and absorbance as well as uniform electrical and optical accesses to each of the nanotubes. The spectral dependence of the photocurrent also allows for an estimate of the band gap of the nanotubes, which is found to be in good agreement with that determined from thermally activated dark conductivity measurements.

Irradiation of thin films of poly(ferrocenylmethylphenylsilane) ([Fe(η5‐C5H4)2SiMePh]n) cast from chloroform solution with UV light leads to photooxidation of ferrocene centers in the polymer main chain. The extent of the polymer oxidation can be controlled in the range ca. 0–5% by the duration of the irradiation exposure and by the concentration of chloroform. The photooxidized polyferrocenylsilane material is conductive, with an increased conductivity of greater than three orders of magnitude relative to the unoxidized material. In addition, the photooxidized polymers have been found to be photoconductive. The photooxidation process can be reversed by means of chemical reduction using hydrazine or decamethylferrocene, leading to the regeneration of the neutral polymers. However, substantial molecular weight decline was detected during the photooxidation/reduction process, presumably as a result of chain cleavage reactions induced by the anionic or radical chlorinated photoproducts. Methylation of the cyclopentadienyl rings of the ferrocene moiety in the polymer was found to lead to materials which are significantly more stable.Time trace of the current at constant applied voltage of 100 V for a PFS film upon illumination. The ON and OFF states were created by using a mechanical shutter.magnified imageTime trace of the current at constant applied voltage of 100 V for a PFS film upon illumination. The ON and OFF states were created by using a mechanical shutter.

We present an infrared (IR) optical absorbance study of highly uniform nanotubes grown by chemical vapor deposition in the self-assembled porous matrix in alumina. For unambiguous IR spectral measurement, nanotubes were extracted from their growth template, purified, and evenly dispersed on a reflecting substrate. The findings, which are consistent with previous results from conduction studies, reveal that the nanotubes are semiconducting with a band gap of ∼100meV. This suggests the potential of nanotube arrays for IR electro-optical device applications.

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