Enrico Trave

Sub-nanometric metallic Au clusters as efficient Er3+ sensitizers in silica

Silica films co-implanted with Er and Au ions show an enhancement of rare earth photoluminescence after gold introduction in the matrix. Er excitation originates in a broad spectral region, from the red to the near ultraviolet. We have investigated the influence of gold aggregation on the optical properties of co-doped samples by varying the temperature of post-Au implantation annealing in the 400–900°C range. Optical measurements and extended x-ray absorption analysis support the hypothesis of an energy transfer process mediated by sub-nanometric Au aggregates with metallic character that are optically activated mostly through electron interband transitions between d and sp-conduction levels.

Strong visible photoluminescence from hollow silica nanoparticles

Starting with crystalline silicon nanoparticles, which were produced by CO2 laser pyrolysis of silane in a gas flow reactor, we have synthesized amorphous silica nanoparticles via oxidation. Upon excitation with UV light, the novel nanostructured material gives rise to an intense red photoluminescence (PL) which resembles that of some silicon nanostructures. Transmission electron microscopy studies and electron energy loss spectroscopy confirm that the nanoparticles are composed of amorphous silica and that the majority of them are hollow. The strong red PL is attributed to defects or molecular species located at the inner and outer surfaces of the hollow nanoparticles. Its similarity to the PL of nanostructured silicon seems fortuitous.

Evidence of energy transfer in an aluminosilicate glass codoped with Si nanoaggregates and Er3+ ions

The enhancement of the Er3+ ions’ photoluminescence (PL) emission at 1.54μm in a Si and Er coimplanted aluminosilicate glass is investigated in detail. A postimplantation thermal treatment has been performed to recover the damage induced by the implantation process and to promote Si aggregation. It will be shown that 1h treatment in N2 atmosphere is not sufficient to induce Si precipitation for temperatures up to 500°C. Nevertheless, the most intense Er3+ PL emission at 1.54μm is achieved after a thermal treatment at 400°C. Such emission has been investigated by pumping in and out of resonance, showing a very efficient energy transfer process in the whole excitation wavelength range (360–515nm). These results suggest that good energy transfer mediators could be small Si aggregates and not only crystalline clusters. For the best performing sample, the effective Er excitation cross section has been measured to be higher than 10−17cm2 at 379 and 390nm and about 2×10−16cm2 at 476nm, that is, several orders of...

Energy transfer in color-tunable water-dispersible Tb–Eu codoped CaF2 nanocrystals

The development of highly luminescent water-dispersible biocompatible nanoparticles is a hot topic in biomedical research. Here, we report about the study of the energy transfer process between Tb3+ and Eu3+ in calcium fluoride nanoparticles. Water-dispersible RE-doped nanoparticles were prepared by means of a simple synthesis route without the need for high temperature, pressure or additional surface functionalization. The structural and morphological properties were investigated by means of XRPD and TEM analysis. Optical analysis led to information about both the RE ion site symmetry in the crystalline host and the Tb3+ and Eu3+ excited state lifetimes, whose remarkable duration is suitable for biosensing applications. Concerning the energy transfer process, dipole–dipole interaction, with a donor–activator critical distance of about 13 A, was identified as the most probable mechanism.

Implantation damage effects on the Er 3+ luminescence in silica

The possibility to control the room temperature Er3+ photoluminescence efficiency in silica is investigated in terms of the damage produced in Er-doped silica by implantations at different fluences with Xe or Au ions. These implantations are tailored to reproduce the same level of damage in Er-doped silica. The remarkable differences in terms of the photoluminescence intensity between Xe- and Au-irradiated samples allowed to decouple the detrimental effect of the implantation damage on the photoluminescence from the beneficial broad-band energy transfer process provided by molecule-like Au clusters formed upon thermal annealing. The evolution of the implantation damage is followed by photoluminescence and correlated to the local Er-site by x-ray absorption spectroscopy.

Doping of silicate glasses with erbium by a field-assisted solid-state ion exchange technique

A field-assisted solid-state ion exchange technique is used for the first time to dope surface layers of silicate glasses with erbium at the concentration of the order of a few 1020 Er cm−3. Rutherford backscattering spectrometry, extended x-ray absorption fine structure spectroscopy and photoluminescence spectroscopy are used to characterize the samples treated after erbium oxide films were formed on soda-lime glass slides.

Sensitizing effects in Ag-Er codoped glasses for optical amplification

A set of samples co-doped with Er and Ag were prepared with a combined sol-gel and ion-exchange route. This multistep process sytnthesizes samples in which the silver atoms are dispersed in the matrix and/or aggregated in Ag multimers or nanoclusters. The samples exhibit a different photo-luminescence response depending on the sensitizing effect due to silver atoms. The spectroscopic properties were correlated with the structural properties investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction. The Er3+ excitation via energy transfer, obtained in a wide range of wavelengths, has been clearly related to the presence in the sample of Ag multimers.

Improved photoluminescence properties of sol-gel derived Er3+ doped silica films

Silica films (amorphous and crystalline) doped with erbium were fabricated on silica glass substrate and characterized. The inorganic-organic hybrid sol-gel method was used to prepare the films and the Na codoping induced the crystallization of silica film. Photoluminescence (PL) measurements revealed that the Er3+ ions can be excited from the ground state through an energy transfer process mediated by active defective sites in SiO2 film matrix. The annealing temperature and atmospheres have large effects on the local environment of Er3+ and the 1.54 μm PL intensity can be improved significantly by suitable heating treatments. We could correlate Er3+ sensitization effect due to the presence of carbon related species in the films. The PL intensity at nonresonant (476.5 nm) condition can be made as intense as the resonant (488 nm) one, for particular annealing conditions. Noticeable changes in PL emission intensities have not been observed whether the matrix silica film is amorphous or crystalline in nature...

Development of an eco-protocol for seaweed chlorophylls extraction and possible applications in dye sensitized solar cells

Seaweeds are a reserve of natural dyes (chlorophylls a, b and c), characterized by low cost and easy supply, without potential environmental load in terms of land subtraction, and also complying with the requirements of an efficient waste management policy. In particular, the brown seaweed Undaria pinnatifida is a species largely present in the Venice Lagoon area, and for it a removal strategy is actually mandatory. In this paper, we set-up an eco-protocol for the best extraction and preparation procedures of the pigment, with the aim of finding an easy and affordable method for chlorophyll c extraction, exploring at the same time the possibility of using these algae within local sustainable management integrated strategies, among which the possible use of chlorophylls as a dye source in dye sensitized solar cells (DSSCs) is investigated. Experimental results suggest that the developed protocols are useful to optimize the chlorophyll c extraction, as shown by optical absorption spectroscopy measurements. The DSSCs built with the chlorophyll extracted by the proposed eco-protocol exhibit solar energy conversion efficiencies are similar to those obtained following extraction protocols with larger environmental impacts.

Strain modification of AlGaN layers using swift heavy ions

Epitaxial AlGaN/GaN layers grown by molecular beam epitaxy (MBE) on SiC substrates were irradiated with 150 MeV Ag ions at a fluence of 5×1012 ions/cm2. The samples used in this study are 50 nm Al0.2Ga0.8N/1 nm AlN/1 μ m GaN/0.1 μ m AlN grown on SI 4H-SiC. Rutherford backscattering spectrometry/channeling strain measurements were carried out on off-normal axis of irradiated and unirradiated samples. In an as-grown sample, AlGaN layer is partially relaxed with a small tensile strain. After irradiation, this strain increases by 0.22% in AlGaN layer. Incident ion energy dependence of dechanneling parameter shows E 1/2 dependence, which corresponds to the dislocations. Defect densities were calculated from the E 1/2 graph. As a result of irradiation, the defect density increased on both GaN and AlGaN layers. The effect of irradiation induced-damages are analyzed as a function of material properties. Observed results from different characterization techniques such as RBS/channeling, high-resolution XRD and AFM are compared and complemented with each other to deduce the information. Possible mechanisms responsible for the observations have been discussed in detail.