M. Tamborra

Optical properties of hybrid composites based on highly luminescent CdS nanocrystals in polymer

High quality luminescent CdS nanocrystals (NCs), with band edge emission tunable in the blue region of the visible spectrum, were synthesized by means of thermal decomposition of precursors with oleic acid as the surfactant and incorporated in optically transparent polystyrene (PS) and poly(methyl methacrylate) (PMMA). The optical properties of the obtained nanocomposite films were investigated by absorption and emission spectroscopies. Enhancement of the band edge luminescence of CdS quantum dots was observed in both polymer matrices and the fluorescence of the composites retained narrow emission profiles. Capping exchange at the NC surface with octylamine, demonstrated to improve the luminescence properties in solution, was performed in order to investigate the role played by surface ligands in the nanocomposite. Octylamine capped NCs immobilized in the polymers showed high defect state emission and visible quenching of band edge luminescence, indicating an effective interaction between oleic acid and PMMA and PS polymeric chains.

Spontaneous emission control of colloidal nanocrystals using nanoimprinted photonic crystals

The authors report on the fabrication and optical characterizations of two-dimensional photonic crystals fabricated by nanoimprint lithography in a nanocomposite polymer incorporating highly luminescent and red emitting (CdSe)ZnS core-shell colloidal nanocrystals. Photonic crystal structures enhance the light emitted from the quantum sized nanoparticles in the composite layer by slowing the propagation speed of the photons, thus increasing the coupling to the out-of-plane radiative modes. A 200% enhancement of the light collection is achieved compared to an unpatterned sample.

Surface chemical functionalization of single walled carbon nanotubes with a bacteriorhodopsin mutant.

In this work, single walled carbon nanotubes (SWNTs) have been chemically functionalized at their walls with a membrane protein, namely the mutated bacteriorhodopsin D96N, integrated in its native archaeal lipid membrane. The modification of the SWNT walls with the mutant has been carried out in different buffer solutions, at pH 5, 7.5 and 9, to investigate the anchoring process, the typical chemical and physical properties of the component materials being dependent on the pH. The SWNTs modified by interactions with bacteriorhodopsin membrane patches have been characterized by UV-vis steady state, Raman and attenuated total reflection Fourier transform infrared spectroscopy and by atomic force and transmission electron microscopy. The investigation shows that the membrane protein patches wrap the carbon walls by tight chemical interactions undergoing a conformational change; such chemical interactions increase the mechanical strength of the SWNTs and promote charge transfers which p-dope the nano-objects. The functionalization, as well as the SWNT doping, is favoured in acid and basic buffer conditions; such buffers make the nanotube walls more reactive, thus catalysing the anchoring of the membrane protein. The direct electron communication among the materials can be exploited for effectively interfacing the transport properties of carbon nanotubes with both molecular recognition capability and photoactivity of the cell membrane for sensing and photoconversion applications upon integration of the achieved hybrid materials in sensors or photovoltaic devices.

Hybrid nanocomposites based on CdS and CdSe colloidal nanocrystals in organic polymers

High quality luminescent CdS and CdSe nanocrystals, with tuneable band edge emission, were synthesized by means of thermal decomposition of precursors in organic solvents, incorporated in polystyrene and poly(methyl methacrylate) and deposited by casting, yielding optically transparent luminescent films. The obtained nanocomposite films were characterized by spectroscopical (UV-vis absorption and emission) and structural (TEM analysis) techniques. The effect of NC composition, concentration, size, and surface chemistry was evaluated in order to understand the role played by such factors in the nanocomposite optical properties for both the investigated polymers. The presence of organic ligand shell was demonstrated to be critical for the NCs incorporation into the polymer matrix.

Nanoimprinted photonic component for light extraction applications

In this paper, the preparation of nanocomposites based on the incorporation of pre-synthesized (CdSe)ZnS core-shell luminescent nanocrystals (NCs) both in a PMMA (poly-methyl methacrylate) homo-polymer and into properly functionalized PMMA co-polymers is discussed. By using this novel luminescent nanocomposite materials, 2D photonic crystals are fabricated by Nanoimprint Lithography (NIL) and characterized, showing an effective enhancement in light extraction, likely to impact the fabrication of high-efficiency LED based on polymers by a cost efficient lithography technique.