P. Prosposito

Performances of the new high quantum efficiency PMTs in DAMA/LIBRA

New dedicated high quantum efficiency (Q.E.) photomultipliers (PMTs) have been produced by HAMAMATSU company, tested, selected and installed in the DAMA/LIBRA set-up at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N.. In this paper the results obtained in the measurements of various features of these high Q.E. PMTs are reported, and some performances of DAMA/LIBRA in this new configuration are shown.

Rigid-cage effects on the optical properties of the dye 3,3′-diethyloxadicarbocyanine incorporated in silica-gel glasses

We investigated the optical properties of the saturable absorber 3,3′-diethyloxadicarbocyanine iodide incorporated in a matrix of silica-gel glass by the sol-gel technique. Absorption, emission, and fluorescence lifetime were studied as functions of the densification procedures. With respect to the liquid solutions, we observed a strong quenching of the P-isomer luminescence and an increase of the N-isomer fluorescence lifetime. These effects are ascribed to a restriction on the molecular photoisomerization rearrangement caused by the rigidity of the silica cage. Moreover, entrapping reduces intermolecular concentration effects. Finally, different from other glass-embedded dyes, both the absorption and the emission are blue-shifted by about 20 nm.

Femtosecond laser selective intramolecular double proton transfer in [2,2'-bipyridyl]-3,3'-diol

Abstract We report an excitation energy dependence of the dynamics of the excited-state intramolecular double-proton transfer of [2,2′-bipyridyl]-3,3′-diol in liquid solution. By means of femtosecond fluorescence upconversion experiments it is shown that an increase of the vibrational energy in the excited electronic S 1 state results in an increase of the ratio of the reaction yields of the monoketo and diketo tautomeric products. The dominance of the concerted double-proton transfer process at the lower excitation energies is evidence for an energy barrier in the dienol–monoketo reaction pathway.

Self-assembled nanoparticles of functional copolymers for photonic applications

A modified emulsion copolymerization of phenylacetylene (PA) with hydrophilic monomers having different functions, i.e., acrylic acid (AA) and N,N-dimethylpropargylamine (DMPA) respectively, yields functionalized polymeric P(PA-co-AA) and P(PA-co-DMPA) nanoparticles. The systematic investigation on the experimental parameters affecting size, surface charge and polydispersity of the copolymers (initiator concentration, reaction time, cosolvent and PA/comonomer ratios) allows to modulate the nanoparticle physico-chemical properties. Spherical shaped particles with diameters in the range 80-500 nm, low polydispersity (PI values in the range 1.11-1.30) and different surface charge densities, between 0.44 and 2.87 microC/cm(2), have been consistently obtained and characterized by means of Dynamic Light Scattering (DLS), laser Doppler electrophoretic and Scanning Electron Microscopy (SEM) studies. XPS measurements have provided information on the nanoparticles chemical surface structure and suggest that AA and DMPA units are preferentially distributed on the surface of the spheres. The nanospheres self-assemble giving large domains (9.5 x 14.5 microm). Photonic analysis of the self-assembled copolymeric nanoparticles has been performed by means of Spectroscopic Ellipsometry (SE) and Bragg reflection spectroscopy, both of them demonstrating a three-dimensional photonic crystal property of these systems.

Fluorescence efficiency of four infrared polymethine dyes

We report on the fluorescence efficiency of four infrared (IR) polymethine dyes. These figures have been determined using an indirect method based on a fluorescence standard (Rhodamine B in ethanol). The fluorescence decay times have been measured too and their correlation with the quantum efficiency data has been shown. The optical behavior of the IR dyes in three solvents with different polarities has been compared and discussed.

Optical investigation of infrared dyes in hybrid thin films

We report on steady-state absorption and emission measurements for two infrared (IR) dye molecules, IR5 and IR1051, incorporated in hybrid organic/inorganic zirconia-based thin films synthesized with a sol-gel technique. For comparison, measurements in liquid solutions have also been carried out, and an estimation of the relative quantum efficiency in solid glassy material with respect to liquid solution is reported. Absorption and emission spectra are discussed in terms of physical and chemical interactions with the host matrix. The present work provides the evidence of successful doping of solid films with dyes for planar waveguides emitting in the infrared region up to 1.3 μm.

Structural changes induced by the catalyst in hybrid sol-gel films: A micro-Raman investigation

Abstract The effect of acid catalysts on the structure and properties of zirconia-based hybrid organic–inorganic thin films obtained by sol–gel, starting from γ-glycidoxypropyl-trimethoxysilane (GLYMO) and zirconium n -propoxide Zr(C 3 H 7 ) 4 , is studied by means of micro-Raman spectroscopy. The kind of network formed during the polymerisation process depends on the catalyst: this modifies the reactivity of the organic moiety of the GLYMO and a glass former behaviour is obtained only when the epoxy ring of the GLYMO is cleaved. Unopened epoxy rings, on the other hand, may protect the guest luminescent molecules, like the azo-dyes, to acid attacks. Nitric and acetic acids are reported as examples.

High-energy angle resolved reflection spectroscopy on three-dimensional photonic crystals of self-organized polymeric nanospheres

We report on the optical characterization of three-dimensional opal-like photonic crystals made by self-organized nanospheres of poly[styrene-(co-2-hydroxyethyl methacrylate)] having a face centred cubic (fcc) structure oriented along the [111] direction. A detailed optical characterization of the samples is presented using angle resolved reflection spectroscopy in specular geometry. The investigated energies are between a/lambda=0.5 and a/lambda=1.5 (where a is the lattice parameter and lambda is the light wavelength), a region in which both first and second-order Bragg diffraction are expected. Some interesting features as branching of the Bragg peak dispersion and high energy reflection peaks are revealed. We compare the experimental data with theoretical calculations using both Bragg diffraction and band structure approach. A comparison with recent results reported in the literature is also presented.

From nanospheres to microribbons: Self-assembled Eosin Y doped PMMA nanoparticles as photonic crystals

A modified emulsion synthesis of poly(methylmethacrylate) (PMMA) with the Eosin Y (EY), commercial chromophore, yields dye doped polymeric nanoparticles (PMMA@EY). A systematic investigation on the experimental parameters (monomer and initiator concentration, reaction time and MMA/EY molar ratio) has been explored to modulate physico-chemical properties of the dye doped polymeric colloids. Spherical shaped particles, doped with EY (0.5-3.0 wt%; loading efficiency η = 11-15%), with controlled diameters in the range 240-510 nm, low dispersity and ζ-potential values in the range between -42 mV and -59 mV, have been synthesized and characterized by means of UV-Vis spectrometry, Dynamic Light Scattering (DLS), laser Doppler electrophoresis and Scanning Electron Microscopy (SEM). Microribbons based on PMMA@EY nanoparticles have been fabricated by room temperature self-assembly of aqueous colloidal suspension on highly wettable glass substrates. Surface chemical treatment assisted the formation of long (up to few centimeters) regular ribbons with rectangular section. Lateral size and height of the structures have been controlled by changing the suspension concentration and/or the deposition volume: the higher suspension concentration produces larger and thicker ribbons and the higher deposited volume produces thicker ribbons (up to 23 μm with 198 μL of a 3 wt% suspension). Moreover, a transition from a film-like to a ribbon-like growth has been observed with increasing nanoparticles concentration. Short range ordering and photonic crystal features have been maintained in the fluorescent ribbon microarchitecture, resulting in a self-assembled material with excellent potential for the development of mirror-less and random lasers.

Organically modified sol–gel films incorporating an infrared dye

Steady-state absorption and emission measurements for an infrared (IR) dye have been reported. Measurements in liquid solutions and in hybrid organic/inorganic zirconia-based thin films synthesized with a sol-gel technique have been carried out. The optical properties of films as a function of the densification temperature have also been investigated. The results are discussed in terms of the presence of monomer and dimer species of the dye and of the physical and chemical interactions with the host matrix.