Enrico Binetti

Spectroscopic study on imidazolium-based ionic liquids: effect of alkyl chain length and anion.

Room temperature ionic liquids are currently used as functional materials in several application and their optical investigation can provide a better understanding of their physical and chemical behavior. Absorption and emission properties of imidazolium-based ILs have been attributed to the imidazolium moiety and related to the presence of energetically different aggregates. Here, time-integrated and time-resolved investigation has been carried out on 1-alkyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids with different chain lengths in order to probe the occurrence of energy transfer processes, and hence to disclose the presence of various states with different energy. Such a study contributes to provide relevant insight on the effect of alkyl chain and anion type on the emission characteristics, and, hence, on the presence of associated structures.

Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

Abstract Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices.

Nanocomposites Based on Luminescent Colloidal Nanocrystals and Polymeric Ionic Liquids towards Optoelectronic Applications

Polymeric ionic liquids (PILs) are an interesting class of polyelectrolytes, merging peculiar physical-chemical features of ionic liquids with the flexibility, mechanical stability and processability typical of polymers. The combination of PILs with colloidal semiconducting nanocrystals leads to novel nanocomposite materials with high potential for batteries and solar cells. We report the synthesis and properties of a hybrid nanocomposite made of colloidal luminescent CdSe nanocrystals incorporated in a novel ex situ synthesized imidazolium-based PIL, namely, either a poly(N-vinyl-3-butylimidazolium hexafluorophosphate) or a homologous PIL functionalized with a thiol end-group exhibiting a chemical affinity with the nanocrystal surface. A capping exchange procedure has been implemented for replacing the pristine organic capping molecules of the colloidal CdSe nanocrystals with inorganic chalcogenide ions, aiming to disperse the nano-objects in the PILs, by using a common polar solvent. The as-prepared nanocomposites have been studied by TEM investigation, UV-Vis, steady-state and time resolved photoluminescence spectroscopy for elucidating the effects of the PIL functionalization on the morphological and optical properties of the nanocomposites.

Semiconductor nanocrystals dispersed in imidazolium-based ionic liquids: a spectroscopic and morphological investigation

A growing interest is devoted to the study of imidazolium-based ionic liquids as innovative materials to combine with functional elements for advanced technological applications. Materials based on semiconductor and oxide nanocrystals in ionic liquids can be promising for their integration in lithium batteries, as well as in innovative solar cells. Although the physical chemical properties and the solvation dynamics of bare ionic liquids have been extensively studied, their combination with colloidal nanocrystals still remains almost unexplored. Here, the optical properties of organic-capped luminescent cadmium selenide nanocrystals coated by a shell of zinc sulfide (CdSe(ZnS)) dispersed in 1,3-dialkyl imidazolium ionic liquids have been investigated, also in dependence of the alkyl chain length on the imidazolium ring and of the anion nature, by using both time-integrated and time-resolved optical spectroscopy. The observed variations in decay profiles of the ionic liquid in presence of colloidal nanocrystals suggest that the dispersion of the nanostructures induces modifications in the ionic liquid structural order. Finally, atomic force microscopy analysis has provided insight into the topography of the investigated dispersions deposited as film, confirming the organization of the ionic liquids in super-structures, also upon nanocrystal incorporation.

Conjugated Polymer and Luminescent Nanocrystals for Ink‐Jet Printing

Nanocomposite solutions formed of Poly [(9,9‐diesilfluorene)‐(2,7 diyl)‐alt‐(2,5‐dimetil‐1,4‐phenilene)] and highly luminescent nanocrystals of CdSe coated with a shell of ZnS (CdSe@ZnS) with different size have been obtained by using a common solvent and characterized by means of absorption and emission spectroscopy. Viscosity has been investigated, in order to prove the suitability of the inks for the printing processing. The homogeneous nanocomposites have been precisely dispensed by ink‐jet printing, using drop‐on‐demand mode onto glass substrates. The deposited micro‐scale pixels have been morphologically characterized by means of fluorescence microscopy, 3D profilometry and Atomic Force Microscopy (AFM). The results demonstrate that the spectroscopical properties of the components have been effectively conveyed to the final nanocomposites, retaining the size dependent feature of the inorganic moiety, and providing a suitable ink with for fabricating reproducible microstructures.

Colloidal synthesis of rare earth-based nanoparticles

Colloidal nanocrystals (NCs) are free-standing nano-sized objects, coordinated by a layer of organic amphiphilic molecules which allows their dispersion in solvents, making easy the manipulation. The organic molecules play a central role in all the synthesis steps by controlling the NC surface during the growth, allowing to obtain a fine control over the size and the shape of NCs. In addition, organic ligands prevent the occurrence of aggregation phenomena. Luminescent NCs, presenting intense emission in the visible and NIR region of the spectra, are of great interest for application in several fields, as optoelectronics and bio-imaging. On the other hand, rare-earth elements, generally in form of trivalent cation, emit sharp-fluorescence peaks which allow their application in bio-imaging and therapeutics. Here, we focused on the synthesis of Gd-based NCs by the “thermal decomposition of organometallic precursor in hot coordinating solvents” using exclusively natural products for each synthetic phase, with the exception for the organometallic NC precursor. In particular, seed oil was used as high-boiling and coordinating solvent and ethanol was used as non-solvent in purification processes. The optical properties of synthesized NCs were monitored by UV-vis absorption and photoluminescence spectroscopy during the NC growth. The morphology of NCs has been monitored by SEM microscopy. Experimental measurement highlighted the formation of Gd-based NCs, 30-40 nm in diameter, characterized by a strong absorption in the UV region of the spectrum and an intense photoluminescence in the green.