Roberto Francini

Emission decay times of F3+ and F2 color centers in LiF crystals

F 3 + and F 2 centers in LiF display efficient broad emissions in the green-red spectral region when excited in their absorption bands located around 450 nm. Recently it has been shown that color centers, impurities and low-dimensionality structures in heavily colored samples influence the optical cycles and in particular the lifetimes of the emitting states. In order to determine these effects we measured the decay times, which are reported in the literature with values scattered by more than a factor 4. We obtained the radiative lifetime To = (8.1 ± 1.2) ns for F + 3 and To = (15.5 ± 0.8) ns for F 2 centers and we did not observe any temperature dependence in the range 15-300 K.

Optical properties of dye-doped sol-gel glasses

We studied the optical properties of three organic dyes (Rhodamine 590, DODCI and IR5) incorporated in sol-gel prepared silica glasses. Absorption and emission spectra and luminescence lifetimes were measured both for as-prepared and for heat-densified samples. The blue shift of the emission peak and the radiative lifetimes increase with the densification of the samples.

Photolithography of 3D Scaffolds for Artificial Tissue

The present study is focused on the design and fabrication of novel functional 3D-hydrogel scaffolds for regenerative medicine. In order to critically analyzing the effect of the microarchitecture of 3D scaffolds for driving the cellular fate and diffusion of progenitor stem cells we have fabricate a number of scaffolds with different geometry, stiffness and composition. The physical characteristics of the scaffold determine indeed, as well the biochemical factors, the fate of the cells. We use an innovative composite material consisting of hydrogel with different molecular weight and with suitable accordion-like and woodpile structures in order to tailor stiffness and elasticity conferred to the final structure.These novel 3D bioinspired scaffolds were obtained by both single- (1PP) and two-photon polymerization (2PP) processing. In particular, 2PP scaffolds represent a great advantage with respect to previous achievements based on traditional methods. 3D-structures were fabricated with lateral resolution of some microns, allowing an advanced control of pore microarchitecture of defined tensile strength, and the inclusion of albumin microspheres with various functionalities. The morphological, biochemical and functional characteristics are discussed. Moreover, the effects of the structured hydrogel scaffolds on the proliferation and differentiation of adult stem cells is analyzed in view of the fabrication of portion of contractile cardiac muscle to be obtained In Vitro.

Anodization-based process for the fabrication of all niobium nitride Josephson junction structures

We studied the growth and oxidation of niobium nitride (NbN) films that we used to fabricate superconductive tunnel junctions. The thin films were deposited by dc reactive magnetron sputtering using a mixture of argon and nitrogen. The process parameters were optimized by monitoring the plasma with an optical spectroscopy technique. This technique allowed us to obtain NbN as well as good quality AlN films and both were used to obtain NbN/AlN/NbN trilayers. Lift-off lithography and selective anodization of the NbN films were used, respectively, to define the main trilayer geometry and/or to separate electrically, different areas of the trilayers. The anodized films were characterized by using Auger spectroscopy to analyze compounds formed on the surface and by means of a nano-indenter in order to investigate its mechanical and adhesion properties. The transport properties of NbN/AlN/NbN Josephson junctions obtained as a result of the above described fabrication process were measured in liquid helium at 4.2 K.

A New Approach for the Spectroscopic Detection of Different pH-Values

The objective of the present work was the development of a micro-pH meter for the determination of the pH value within bioreactors with a volume of up to 200 μl in total. Two different prototypes of optodes were designed and tested. In a first approach spectroscopic analysis of bromothymol blue in a micro-sized-channel structure was carried out utilizing glass fibers, enabling measurements in sample volumes down to the range of picoliters. In a second approach a different illumination system consisting of a RGB-sensor and a LED light source was used. Phenol red was successfully applied as the pH indicator for this setup.

Photonic application of diatom frustules

Diatoms are unicellular aquatic microalgae possessing amazing self-assembled ordered micro-and nanoporous hierarchical silica cell walls called frustules. The quasi-periodic and highly regular pore patterns on the diatom surface are very attractive for applications based on optical and photonic properties of materials. The present contribution reports on pioneering research aimed at explore the multiple scattering and localization of light shown by diatom frustules in order to amplify their photoluminescence in a random laser (RL), as this technology is highly attractive for medical diagnostics and other advanced applications. RL is a special type of laser in which the optical feedback is due to light scattering in an amplifying medium instead of a conventional optical cavity. We have studied a set of selected frustules with different shapes and pore patterns, obtained from diatom cultivation in large scale photobioreactors, for comparative analysis of their random lasing effect in the bioscaffold soaked with organic dyes having luminescence in the visible range. Taking advantage from a multidisciplinary approach combining expertise from biology, physics and materials sciences, relying on high-resolution instrumentation and advanced algal cultivation equipment the results about random laser emission in the composite material were obtained. This will allow going ahead in the research aimed to the application to photonic devices in the field of medicine and medical diagnostic.