Green Synthesis of Iridium Nanoparticles from Winery Waste and Their Catalytic Effectiveness in Water Decontamination

An environmentally friendly procedure was adopted for the first time to prepare green iridium nanoparticles starting from grape marc extracts. Grape marcs, waste of Negramaro winery production, were subjected to aqueous thermal extraction at different temperatures (45, 65, 80, and 100 °C) and characterized in terms of total phenolic contents, reducing sugars, and antioxidant activity. The results obtained showed an important effect of temperature with higher amounts of polyphenols and reducing sugars and antioxidant activity in the extracts with the increase of temperature. All four extracts were used as starting materials to synthesize different iridium nanoparticles (Ir-NP1, Ir-NP2, Ir-NP3, and Ir-NP4) that were characterized by Uv-Vis spectroscopy, transmission electron microscopy, and dynamic light scattering. TEM analysis revealed the presence of very small particles in all samples with sizes in the range of 3.0–4.5 nm with the presence of a second fraction of larger nanoparticles (7.5–17.0 nm) for Ir-NPs prepared with extracts obtained at higher temperatures (Ir-NP3 and Ir-NP4). Since the wastewater remediation of toxic organic contaminants on catalytic reduction has gained much attention, the application of the prepared Ir-NPs as catalysts towards the reduction of methylene blue (MB), chosen as the organic dye model, was evaluated. The efficient catalytic activity of Ir-NPs in the reduction of MB by NaBH4 was demonstrated and Ir-NP2 was prepared using the extract obtained at 65 °C, showing the best catalytic performance, with a rate constant of 0.527 ± 0.012 min−1 and MB reduction of 96.1% in just six min, with stability for over 10 months

Nanopatterning of colloidal nanocrystals emitters dispersed in a PMMA matrix by e-beam lithography

We report on the fabrication of periodic nanostructures embedding semiconductor colloidal nanocrystals (NCs) by directly exposing a polymer/NCs blend to electron beam lithography (EBL). Our technological approach for the fabrication of NCs-based photonic devices relies on the dispersion of CdSe/ZnS core/shell NCs into a layer of polymethilmethacrylate (PMMA) positive electron resist, which is patterned by means of an EBL process. The presence of NCs in the resist did not modify the peculiar behaviour of PMMA, which was selectively removed from the regions exposed to the electron beam. The morphology of the sample was assessed by scanning electron microscopy and atomic force microscopy measurements. The optical analysis of the samples after the dispersion of the NCs into the PMMA matrix and the exposure to the e-beam showed the successful localization of the colloidal NCs, whose emission properties were preserved

Multicolored devices fabricated by direct lithography of colloidal nanocrystals

Colloidal nanocrystals (NCs) are interesting as potential active medium for novel nanophotonic and nanoelectronic devices, due to their low fabrication costs and full tunability of their opto-electronic properties. In this work we report a multi step approach for the fabrication of multicolored micro- and nano- displays by localizing NCs through lithographic techniques without recurring to etching processes or surface treatment of the substrate. We demonstrate the possibility to localize different ensembles of emitters on the same substrate by realigned photolithographic steps or mix-and-match electron beam and photolithographic approaches. Moreover, fine tuning of the overall pixel emission is shown by varying the concentration ratio among localized red and green NCs. This technique enables the fabrication of optically pumped colored pixels with very high definition. Our approach combined with advances in NCs-based light emitting diodes technology will enable the electrical injection of advanced micro and nano light sources

High-Purcell-factor dipolelike modes at visible wavelengths in H1 photonic crystal cavity

The optimization of H1 photonic crystal cavities for applications in the visible spectral range is reported, with the goal to obtain a versatile photonic platform to explore strongly and weakly coupled systems. The resonators have been realized in silicon nitride and weakly coupled to both organic (fluorophores) and inorganic (colloidal nanocrystals) nanoparticles emitting in the visible spectral range. The theoretical Purcell factor of the two dipolelike modes in the defect has been increased up to approximately 90, and the experimental quality factor was measured to be approximately 750

Design and modeling of χ(2) second harmonic amplification in circular photonic crystal

We analyze in this work the second harmonic amplification of χ(2) nonlinear process in membrane type GaAs circular photonic crystal. This unconventional kind of photonic crystal is well suited for the generation of whispering gallery modes due to the circular symmetric periodic pattern. The Gaussian beam of a fundamental pump signal at 1.55 μm defines a whispering gallery mode resonance and generates a second harmonic mode at 0.775 μm in the central missing hole micro-cavity. The periodic pattern and the micro-cavity are tailored and optimized in order to generate a second harmonic conversion efficiency of 50 %. We predict the resonances by an accurate 2D time domain model including χ(2) nonlinearity and also by a 3D Finite Element Method FEM. Moreover, by using a 3D membrane configuration, we predict a quality factor of the second harmonic mode of the order of 35000

Single colloidal quantum dots as sources of single photons for quantum cryptography

Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature single photon sources for quantum information and quantum telecommunications

Silicon nitride PhC nanocavities as versatile platform for visible spectral range devices

Abstract We propose silicon nitride two-dimensional photonic crystal resonators as flexible platform to realize photonic devices based on spontaneous emission engineering of nanoemitters in the visible spectral range. The versatility of our approach is demonstrated by coupling the two dipole-like modes of a closed band gap H1 nanocavity with: (i) DNA strands marked with Cyanine 3 organic dyes, (ii) antibodies bounded to fluorescent proteins and (iii) colloidal semiconductor nanocrystals localized in the maximum of the resonant electric field. The experimental results are in good agreement with the numerical simulations, highlighting the good coupling of the nanocavities with both organic and inorganic light emitters

Spectral tagging by integrated photonic crystal resonators for highly sensitive and parallel detection in biochips

We propose a technological approach aimed at improving biochips performances, based on an efficient spectral modeling and enhancement of markers fluorescence through the insertion of photonic crystal nanocavities (PhC-NCs) in the readout area of biochips. This strategy univocally associates a specific emission wavelength to a specific bioprobe immobilized on a nanocavity, therefore guaranteeing parallel detection of multiple elements and faster analysis time. Moreover, PhC-NCs significantly enhance the markers fluorescence, thus improving the detection sensitivity

Optical filter based on two coupled PhC GaAs-membranes.

We demonstrate an ultracompact optical filter based on two coupled high-index contrast GaAs photonic crystal (PhC) membranes. The PhC membranes consist of a square lattice of air holes and behave as a Fabry-Perot cavity whose reflectivity and transmissivity depend on the air gap between the two membranes. The normal-incidence reflectance measurements and the numerical simulation of reflection spectra show a high sensitivity to the geometrical parameters, such as the distance between the slabs, whose control would make the device suitable for a new class of tunable optical filters