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In order to best nutrient use efficiency, as required by the increasing food demand for the future global population, in this work an innovative hybrid nanocomposite was designed as an alternative nanoscale fertilizer. An environmentally friendly chemical preparation based on polyelectrolyte complexation was used. A chitosan and sodium alginate complex was selected as a biodegradable shell to release the nanoscale nutrient, CuO nanoparticles. By optimizing the synthesis conditions, i.e. pH and polymer/cross-linker ratio, good stability and accurate size control of the resulting nanocomposites were achieved. The morphology features were evaluated using scanning and transmission electron microscopy, and chemical characterization was performed using X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, dynamic light scattering and inductively coupled plasma optical emission spectrometry. All the collected data confirmed spontaneous polymeric aggregation in nanostructures of sperical shape, having a mean diameter of about 300 nm, as well as CuO encapsulation inside the polymeric coating. Moreover, the role of the biopolymer shell in the significant slowing of copper release from the hybrid nanocomposite was reported. Finally, the nanocomposite efficacy in seeding and germination was evaluated on Fortunella margarita Swingle seeds. The tests demonstrated the benefits in the seedling growth together with a synergic effect in developing both the epigean and hypogean parts. The obtained results indicated that the proposed hybrid nanocomposite could be a potential alternative to realize a smart delivery nanofertilizer using an eco-sustainable method.

Disordered materials with new optical properties are capturing the interest of the scientific community due to the observation of innovative phenomena. We present the realization of novel optical materials obtained by fractal arrays of silicon nanowires (NWs) synthesized at low cost, without mask or lithography processes and decorated with Er:Y2O3, one of the most promising material for the integration of erbium in photonics. The investigated structural properties of the fractal Er:Y2O3/NWs demonstrate that the fractal morphology can be tuned as a function of the sputtering deposition angle (from 5° to 15°) of the Er:Y2O3 layer. We demonstrate that by this novel approach, it is possible to simply change the Er emission intensity by controlling the fractal morphology. Indeed, we achieved the increment of Er emission at 560 nm, opening new perspectives on the control and enhancement of the optical response of novel disordered materials.

A fractal array of room-temperature (RT) luminescent Si nanowires (NWs) is realized by thin-film metal-assisted chemical etching, a cost-effective, fast, and maskless Si technology compatible approach. This process permits obtaining Si NWs with interesting structural and optical features for a wide range of applications, from photonics to sensing. For what concern photonics, the possibility to fabricate artificial fractals based on Si NWs that integrate other interesting elements is reported. In particular, an artificial fractal based on the Er:Y2O3 decoration of Si NWs where the Er emission can be tuned as a function of the decoration angle is shown. In the sensor field, the use of Si NW luminescence can represent an interesting and innovative sensing mechanism for the realization of a novel class of sensing platform. In this work, a light-emitting Si NWs-based label-free sensor for both selective isolation and ultrasensitive quantification of small extracellular vesicles (sEVs) is reported opening the route toward liquid biopsy applications.

Erbium-doped Si nanowires fractals arise as promising photonic platforms for integrated devices due to their tunable optical response. The coherent propagation of light combined with quantum effects foster novel perspectives for light management.

Silicon nanowires (Si NWs) emerged in several application fields as a strategic element to surpass the bulk limits with a flat compatible architecture. The approaches used for the Si NW realization have a crucial impact on their final performances and their final cost. This makes the research on a novel and flexible approach for Si NW fabrication a crucial point for Si NW-based devices. In this work, the novelty is the study of the flexibility of thin film metal-assisted chemical etching (MACE) for the fabrication of Si NWs with the possibility of realizing different doped Si NWs, and even a longitudinal heterojunction p-n inside the same single wire. This point has never been reported by using thin metal film MACE. In particular, we will show how this approach permits one to obtain a high density of vertically aligned Si NWs with the same doping of the substrate and without any particular constraint on doping type and level. Fractal arrays of Si NWs can be fabricated without any type of mask thanks to the self-assembly of gold at percolative conditions. This Si NW fractal array can be used as a substrate to realize controllable artificial fractals, integrating other interesting elements with a cost-effective microelectronics compatible approach.

Although in the last decades rare earths (REs)-containing materials have been proposed as active media in Si compatible light sources, the reached optical efficiency is still limited by the low REs excitation cross section. In this work, the introduction of Bi as an Er sensitizer in a Si-compatible yttrium oxide thin film has been proposed in order to overcome this limit. The stabilization of optically active Bi3+ ions in place of Y3+ in the two reticular sites, S-6 and C-2, of Y2O3 was demonstrated. Photoluminescence (PL) and photoluminescence excitation measurements have revealed the existence of two different intense emission bands in the visible range ascribed to Bi3+ in the two reticular sites. They can be selectively excited by properly changing the excitation wavelength. Moreover, the Bi3+-> Er3+ energy transfer processes in the (Bi+Er)-codoped samples were demonstrated for both Bi3+ sites by the spectral overlap between the Bi emission bands and Er excitation peaks. We estimated an Er emission enhancement by a factor of about 80 for the C-2 site and 16 for the S-6 site with respect to the Er direct excitation. By the recorded reduction of the Bi PL intensities and the shortening of the related lifetimes in presence of Er ions, the energy transfer efficiencies were evaluated to be about 70% for the Bi (C-2) and 35% for the Bi (S-6). These interesting findings suggest (Bi+Er)-codoped yttrium oxide as an efficient Si-compatible material for photonic applications. (C) 2016 Elsevier B.V. All rights reserved.

Here we report the photocatalytic efficiency of hydrogenated TiO2 nanoplumes studied by measuring dye degradation in water. Nanoplumes were synthesized by peroxide etching of Ti films with different thicknesses. Structural characterization was carried out by scanning electron microscopy and transmission electron microscopy. We investigated in detail the optical properties of the synthesized material and related them to the efficiency of UV photodegradation of methylene blue dye. The obtained results show that TiO2 nanoplumes act as an effective antireflective layer increasing the UV photocatalytic yield of the film.

A novel hybrid photoactive material based on graphene foam (G) coupled with porphyrin-based polymers (Porph rings) was formulated by using a time-saving procedure to remove nickel from the final device. Specifically, Porph rings were spin coated onto the G platform with the double function of a visible-light photocatalyst and protective agent during nickel etching. The characterization of G-Porph rings was assessed by Scanning Electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). The novel material showed photocatalytic ability in degrading different classes of pollutants such as the herbicide 2,4 dichlorophenoxyacetic acid (2,4-D), polyethylene glycol (PEG) as an ingredient of care and health products, and also the methylene blue (MB) dye. UV-Vis spectroscopy, total organic carbon (TOC) and soft mass spectrometry techniques were used to monitor the photocatalytic process. The best performance in terms of photocatalytic efficiency was exhibited versus PEG and MB degradation. Furthermore, to determine the individual contribution of Reactive Oxygen Species (ROS) produced, free radical and hole scavenging tests were also carried out. Finally, a detailed map of the photocatalytic degradation mechanisms was proposed, reporting also the calculation of Porph rings' Highest Occupied Molecular Orbital (HOMO) and Lowest Occupied Molecular Orbital (LUMO) energy level values.

In the last decades, in the field of silicon microphotonics many efforts have been made to find strategies in order to obtain efficient luminescence from silicon or from Si compatible materials that could be totally integrated on Si microchips. Among the several approaches, mixed rare earth silicates and oxides have received great attention as active media, owing to their compatibility with the standard Si technology and the possibility to dissolve inside high concentrations of luminescent centers. In this paper we will review the last achievements on the investigation of the structural and optical properties of erbium doped yttrium silicates and oxides. We will further show the advantages of using bismuth as Er co-dopant, as strategy to improve optical efficiency at 1540 nm, wavelength of interest for telecommunications. The stabilization and the role of the Bi3+ oxidation state will be evidenced along the paper by comparing the results of the Bi influence on the Er emission in the two hosts. Photoluminescence in excitation measurements will permit to demonstrate that Bi ions act as efficient sensitizers to transfer energy to Er ions. Hence, through mediated excitation the Er excitation cross section is increased up to two or three orders of magnitude in silicates and oxide, respectively, if compared to the Er resonant condition at 488 nm. In the second part of the paper we will focus on the investigation of Bi doped yttrium oxide as efficient visible emitter. In particular, the peculiar dependence of the Bi emission on the excitation wavelength, which makes the Bi-doped oxide a tunable light source, together with the estimation of its optical efficiency, permits to clearly evidence its potentiality for application in visible light emitting devices.

The direct observation of high-energy cosmic rays, up to the PeV region, will increasingly rely on highly performing calorimeters, and the physics performance will be primarily determined by their geometrical acceptance and energy resolution. Thus, it is extremely important to optimize their geometrical design, granularity, and absorption depth, with respect to the total mass of the apparatus, which is among the most important constraints for a space mission. Calocube is a homogeneous calorimeter whose basic geometry is cubic and isotropic, so as to detect particles arriving from every direction in space, thus maximizing the acceptance; granularity is obtained by filling the cubic volume with small cubic scintillating crystals. This design forms the basis of a three-year R & D activity which has been approved and financed by INFN. A comparative study of different scintillating materials has been performed. Optimal values for the size of the crystals and spacing among them have been studied. Different geometries, besides the cubic one, and the possibility to implement dual-readout techniques have been investigated. A prototype, instrumented with CsI(Tl) cubic crystals, has been constructed and tested with particle beams. An overview of the obtained results will be presented and the perspectives for future space experiments will be discussed.

CaloCube is an R&D project borne to develop a novel calorimeter design, optimized for high-energy cosmic ray measurements in space. A small prototype made of CsI(Tl) elements has been built and tested on particle beams. A final version, made of 5×5×18 crystals and with dual readout (two photodiodes for each crystal), to cover the full required dynamic range, is under construction and will be tested at CERN SPS in Summer 2016. The dual readout compensation technique were developed and the feasibility to extract ÄŒ erenkov signals from CsI crystals verified.

The direct measurement of the cosmic-ray spectrum, up to the knee region, is one of the instrumental challenges for next generation space experiments. The main issue for these measurements is a steeply falling spectrum with increasing energy, so the physics performance of the space calorimeters are primarily determined by their geometrical acceptance and energy resolution. CaloCube is a three-year R&D; project, approved and financed by INFN in 2014, aiming to optimize the design of a space-born calorimeter. The peculiarity of the design of CaloCube is its capability of detecting particles coming from any direction, and not only those on its upper surface. To ensure that the quality of the measurement does not depend on the arrival direction of the particles, the calorimeter will be designed as homogeneous and isotropic as possible. In addition, to achieve a high discrimination power for hadrons and nuclei with respect to electrons, the sensitive elements of the calorimeter need to have a fine 3-D sampling capability. In order to optimize the detector performances with respect to the total mass of the apparatus, which is the most important constraint for a space launch, a comparative study of different scintillating materials has been performed using detailed Monte Carlo simulation based on the FLUKA package. In parallel to simulation studies, a prototype consisting in 14 layers of 3 x 3 CsI(Tl) crystals per layer has been assembled and tested with particle beams. An overview of the obtained results during the first two years of the project will be presented and the future of the detector will be discussed too.

Silicon nanophotonics is emerging as a new platform for the integration of photonic and electronic devices. Several examples on our recent efforts on monolithic light sources based on silicon nanostructures will be presented and discussed. In particular it will be shown that silicon-oninsulator (SOI) is emerging as an interesting photonic material. A first example of a photonic nanostructure on SOI for the control of light emission has been a “slot” waveguide. It is a slab waveguide having a very thin layer (slot) of low refractive index material (SiO2) embedded within a high refractive index one (Si), the core. It gives rise to a strong enhancement of the electromagnetic field in the slot. Then when Er-doped Si nanoclusters are embedded in the silica thin layer a very strong enhancement of guided photoluminescence is observed. Also the enhancement in the spontaneous emission rate is involved, similar to the Purcell effect of an emitter in an optical cavity, as demonstrated by calculations [1]. Another promising approach is represented by the integration of this singular slot waveguide to a photonic crystal (PhC), that permits to accurately tailor the light propagation and confinement by a periodic modulation of the dielectric constant. Simultaneous inhibition and redistribution of light emission in these systems have permitted to obtain an enhancement of the Er nearnormal emission when the involved transition is in resonance with an appropriate mode of the PhC slab both under optical and electrical excitation. Therefore the realized electroluminescent devices on SOI platform (see an image in Fig.1) based on the coupling of efficient emitters, such as Er-doped Si nanoclusters, and the photonic modes of a proper photonic structure have permitted to obtain very high external efficiency, by making these devices very promising.

For many decades, rare earths (REs) doped compounds have attracted considerable interest as emitting materials for displays and photonics applications. However, owing to the difficulty in achieving strongly efficient RE-doped emitting devices, the researchers interest is moving towards other solutions. The use of post-transition metals, such as bismuth, as dopants for Si-compatible materials is one of them. In this work, the dissolution of optically active Bi ions in RE compounds will be illustrated and its properties as visible emitter and as an Er sensitizer for infrared emission will be addressed.

Here we report the photocatalytic efficiency of hydrogenated TiO2 nanoplumes studied by measuring dye degradation in water. Nanoplumes were synthesized by peroxide etching of Ti films with different thicknesses. Structural characterization was carried out by scanning electron microscopy and transmission electron microscopy. We investigated in detail the optical properties of the synthesized material and related them to the efficiency of UV photodegradation of methylene blue dye. The obtained results show that TiO2 nanoplumes act as an effective antireflective layer increasing the UV photocatalytic yield of the film.

Powders of yttrium disilicate (Y2Si2O7) doped with Er3+ have been prepared by the sol-gel method. The structure of the obtained powders has been determined. Room temperature emission spectra have been recorded and excited state decay profiles have been analyzed. Differences between the spectroscopic properties of Er3+ in monoclinic alpha-Y2Si2O7 (space group P-1) and beta-Y2Si2O7 (space group C2/m) polymorphs have been investigated and shown. The significant broadening of the emission spectra recorded for the alpha phase compared to the one for the beta phase was discussed in terms of higher number of Y3+ sites (4) present in the alpha phase with respect to only one Y3+ site in the case of beta phase. The higher value of the luminescence decay time of beta phase (11.2 ms) compared to the alpha phase (8.5 ms) is associated with the higher site symmetry of beta-Y2Si2O7. Moreover it was found that Er3+ concentration affects the shape of the I-4(13/2) -> I-4(15/2) emission band. It results in changes of the relative emission intensities of peaks localized at 1527 nm and 1532 nm; this indicates changes of the Y3+ sites occupation on increasing the Er3+ concentration. The luminescence lifetime was observed to decrease with the increase of Er3+ concentration. The spectroscopic results have been compared with the ones relative to thin films of Y2Si2O7:Er3+ with a similar composition. The lower value of the luminescence decay time observed for thin films compared to the powder of alpha phase was explained with the changes of the particles packing resulting in the change of the effective refractive index. (C) 2015 Elsevier B.V. All rights reserved.

Er-containing silicon compatible materials have been widely used as infrared emitters for microphotonics application. In this field, the additional introduction of a proper sensitizer permits to increase the Er excitation cross sections, thus increasing its optical efficiency. This work aims to investigate the influence of a post-transition metal, bismuth, on the optical properties of erbium-yttrium disilicate thin films synthesized by magnetron co-sputtering. After thermal treatments at 1000 °C in O2 or N2 environment, the presence of small precipitates, about 6 nm in diameter, was evidenced by transmission electron microscopy analyses. The spatially resolved chemical nature of the nanoparticles was discerned in the Si and O rich environments by means of scanning transmission electron microscopy–energy dispersive X-ray and scanning transmission electron microscopy–electron energy loss spectroscopy analyses performed with nanometric resolution. In particular, metallic Bi nanoparticles were stabilized in the N2 environment, being strongly detrimental for the Er emission. A different scenario was instead observed in O2, where the formation of Bi silicate nanoparticles was demonstrated with the support of photoluminescence excitation spectroscopy. In particular, a broad band peaked at 255 nm, correlated to the excitation band of Bi silicate nanoparticles, was identified in Er excitation spectrum. Thus Bi silicate clusters act as sensitizer for Er ions, permitting to improve Er emission up to 250 times with respect to the resonant condition. Moreover, the Er decay time increases in the presence of the Bi silicate nanoparticles that act as cages for Er ions. These last results permit to further increase Er optical efficiency in the infrared range, suggesting (Bi + Er)-Y disilicate as a good candidate for applications in microphotonics.

A large-scale use of nanotechnology for photocatalysis-based water purification requires to identify simple, reliable and low cost processes for the production of the photocatalytic materials. To this aim we have investigated the possibility to deposit, by electrophoresis, composite layers formed by multi-walled carbon nanotubes (MWCNTs) and anatase-type titanium dioxide nanoparticles (np-TiO2), with different weight ratios. This method allows one to obtain photocatalytic layers on any conductive substrates that in principle can be re-used several times. The photocatalytic efficiency for each C-nanostructure/np-TiO2 composite layer is evaluated by measuring the degradation of methylene blue (MB) dye induced by the light of a solar simulator or UVA/blue light irradiation. The morphology and the composition of the deposited layers are studied by scanning electron microscopy and energy dispersive X-ray analyses, respectively, while photoluminescence spectra were acquired in order to explain the different photocatalytic behaviors observed for each material.

The structural, optical and electrical properties of sputtered cuprous oxide thin films have been optimized through post-deposition thermal treatments. Moreover we have studied the effects of nitrogen doping introduced by ion implantation followed by the optimized oxidant thermal annealing. Three concentrations have been used, 0.6 N%, 1.2 N%, and 2.5 N%. Along with the preservation of the Cu 2 O phase, a slight optical band gap narrowing and a significant conductivity enhancement has been observed with respect to the undoped samples. These results can be justified by the absence of further oxygen vacancies promoted by dopant introduction and by the substitution of O atoms by N ones. This lattice configuration has been guaranteed by the post implantation annealing in oxidant atmosphere. The used doping technique represents an original out-of-equilibrium approach toward the formation of low-resistivity contacts on Cu 2 O films for photovoltaic applications.

Future research in High Energy Cosmic Ray Physics concerns fundamental questions on their origin, acceleration mechanism, and composition. Unambiguous measurements of the energy spectra and of the composition of cosmic rays at the “knee” region could provide some of the answers to the above questions. Only ground based observations, which rely on sophisticated models describing high energy interactions in the earth׳s atmosphere, have been possible so far due to the extremely low particle rates at these energies. A calorimeter based space experiment can provide not only flux measurements but also energy spectra and particle identification, especially when coupled to a dE/dx measuring detector, and thus overcome some of the limitations plaguing ground based experiments. For this to be possible very large acceptances are needed if enough statistic is to be collected in a reasonable time. This contrasts with the lightness and compactness requirements for space based experiments. A novel idea in calorimetry is discussed here which addresses these issues while limiting the mass and volume of the detector. In fact a small prototype is currently being built and tested with ions. In this paper the results obtained will be presented in light of the simulations performed.

In this study we employed hydrogen peroxide etching of Ti films as a straightforward method to synthesize hydrogenated TiO2 nanoplumes. The material was extensively characterized, showing, among other special features, the inclusion of OH groups. These groups together with the generated structural defects and the nanostructuration are crucial for the high photocatalytic properties under ultraviolet (UV) and visible (VIS) light irradiation. In particular, nanoplumes show a reaction rate about 5 times the rate of TiO2 flat films. Furthermore, nanoplumes display a significant antibacterial activity under VIS light irradiation, compared with TiO2 films.

Here we report the photocatalytic efficiency of CuO and Cu2O nanowires studied by dye degradation in water. The CuO nanowires were synthesized on Cu foils by thermal oxidation. A subsequent thermal annealing induced a controllable phase transformation of the nanowires and the underlying film from CuO to Cu2O phase. A structural characterization was made by scanning and transmission electron microscopies, energy dispersive x-ray analysis and x-ray diffraction. The photocatalytic performances were evaluated by the degradation of two dyes in water: methylene blue and methyl orange. In particular, CuO nanowires showed a good photocatalytic activity in degrading methyl orange, compared with Cu2O nanowires. The photocatalytic activity was correlated to the physical-chemical properties of the samples, revealing the detrimental effect of the polycrystalline structure for photocatalytic process.

We report about the synthesis of rutile TiO2 nanowires (NWs) by thermal oxidation (700 degrees C for 4 h in a mixed flow of argon and oxygen) of a sputtered titanium thin film (325 nm) on glass substrate covered by a thin layer of gold as catalyzer. We studied the morphological and structural characteristics of the sample by scanning electron microscopy and Rutherford backscattering analyses. NWs are uniformly distributed on the surface with size up to 500 nm in length and up to 100 nm in diameter. We investigated the photocatalytic activity and the photonic efficiency in the degradation of the Methilene Blue (MB) dye. In order to remark the contribution of the NWs in the process, we compared the photocatalytic activity with the one of the annealed TiO2 thin film substrate without NWs. The photocatalytic rate per Unit area for the sample with and without NWs resulted to be (2.52 +/- 0.06).10(-3) cm(-2) min(-1) and (1.26 +/- 0.02). 10(-3) cm(-2) min(-1), respectively; the photonic efficiency (in %) of the MB degradation was estimated as 0.021 +/- 0.006 and 0.021 +/- 0.006, respectively. These results suggest an improvement of the photocatalytic properties due to the presence of the TiO2 NWs on the film. (C) 2015 Elsevier Ltd. All rights reserved.

In the present article we report enhanced light absorption, tunable size-dependent blue shift, and efficient electron hole pairs generation in Ge nanoporous films (np-Ge) grown on Si. The Ge films are grown by sputtering and molecular beam epitaxy; subsequently, the nanoporous structure is obtained by Ge+ self-implantation. We show, by surface photovoltage spectroscopy measurements, blue shift of the optical energy gap and strong signal enhancement effects in the np-Ge films. The blue shift is related to quantum confinement effects at the wall separating the pore in the structure, the signal enhancement to multiple light-scattering events, which result in enhanced absorption. All these characteristics are highly stable with time. These findings demonstrate that nanoporous Ge films can be very promising for photovoltaic applications.

Quantum confinement (QC) typically assumes a sharp interface between a nanostructure and its environment, leading to an abrupt change in the potential for confined electrons and holes. When the interface is not ideally sharp and clean, significant deviations from the QC rule appear and other parameters beyond the nanostructure size play a considerable role. In this work we elucidate the role of the interface on QC in Ge quantum dots (QDs) synthesized by rf-magnetron sputtering or plasma enhanced chemical vapor deposition (PECVD). Through a detailed electron energy loss spectroscopy (EELS) analysis we investigated the structural and chemical properties of QD interfaces. PECVD QDs exhibit a sharper interface compared to sputter ones, which also evidences a larger contribution of mixed Ge-oxide states. Such a difference strongly modifies the QC strength, as experimentally verified by light absorption spectroscopy. A large size-tuning of the optical bandgap and an increase in the oscillator strength occur when the interface is sharp. A spatially dependent effective mass (SPDEM) model is employed to account for the interface difference between Ge QDs, pointing out a larger reduction in the exciton effective mass in the sharper interface case. These results add new insights into the role of interfaces on confined systems, and open the route for reliable exploitation of QC effects. © The Royal Society of Chemistry.

The structural transformations occurring in Ge2Sb2Te5 films heated at temperature up to 400 °C, and under hydrostatic pressure up to 12 GPa, have been investigated through in-situ X ray diffraction measurements. The adopted experimental conditions are close to those experienced by the phase change material during the SET (crystallization)/RESET (amorphization) processes in a nonvolatile memory device. The compression enhances the thermal stability of the amorphous phase, which remains stable up to 180 °C at 8 GPa and to 230 °C at 12 GPa. The structure of the crystalline phases is also modified, with the formation of a CsCl-type structure instead of rock-salt and of a GeS-type structure at the temperature at which usually the trigonal stable phase is formed. Overall, the stability of the stable phase appears to be more affected by the compression. We argue that the presence of weak bonds associated to the van der Waals gaps is a determining factor for the observed reduced stability.

Future space experiments dedicated to the observation of high-energy gamma and cosmic rays will increasingly rely on a highly performing calorimetry apparatus, and their physics performance will be primarily determined by the geometrical dimensions and the energy resolution of the calorimeter deployed. Thus it is extremely important to optimize its geometrical acceptance, the granularity, and its absorption depth for the measurement of the particle energy with respect to the total mass of the apparatus which is the most important constraint for a space launch. The proposed design tries to satisfy these criteria while staying within a total mass budget of about 1.6 tons. Calocube is a homogeneous calorimeter instrumented with Cesium iodide (CsI) crystals, whose geometry is cubic and isotropic, so as to detect particles arriving from every direction in space, thus maximizing the acceptance, granularity is obtained by filling the cubic volume with small cubic CsI crystals. The total radiation length in any direction is more than adequate for optimal electromagnetic particle identification and energy measurement, whilst the interaction length is at least suficient to allow a precise reconstruction of hadronic showers. Optimal values for the size of the crystals and spacing among them have been studied. The design forms the basis of a three-year R&D; activity which has been approved and financed by INFN. An overall description of the system, as well as results from preliminary tests on particle beams will be described.

The process of energy transfer (ET) between optically active ions has been widely studied to improve the optical efficiency of a system for different applications, from lighting and photovoltaics to silicon microphotonics. In this work, we report the influence of Bi on the Er optical emission in erbium-yttrium oxide thin films synthesized by magnetron co-sputtering. We demonstrate that this host permits to well dissolve Er and Bi ions, avoiding their clustering, and thus to stabilize the optically active Er3+ and Bi3+ valence states. In addition, we establish the ET occurrence from Bi3+ to Er3+ by the observed Bi3+ PL emission decrease and the simultaneous Er3+ photoluminescence (PL) emission increase. This was further confirmed by the coincidence of the Er3+ and Bi3+ excitation bands, analyzed by PL excitation spectroscopy. By increasing the Bi content of two orders of magnitude inside the host, though the occurrence of Bi-Bi interactions becomes deleterious for Bi3+ optical efficiency, the ET process between Bi3+ and Er3+ is still prevalent. We estimate ET efficiency of 70% for the optimized Bi:Er ratio equal to 1:3. Moreover, we have demonstrated to enhance the Er3+ effective excitation cross section by more than three orders of magnitude with respect to the direct one, estimating a value of 5.3 x 10(-18) cm(2), similar to the expected Bi3+ excitation cross section. This value is one of the highest obtained for Er in Si compatible hosts. These results make this material very promising as an efficient emitter for Si-compatible photonics devices. (C) 2015 AIP Publishing LLC.

The structural properties and the room temperature luminescence of Er 2 O 3 thin films deposited by RF magnetron sputtering have been studied. Films characterized by good morphological properties have been obtained by using a SiO 2 interlayer between the film and the Si substrate. The evolution of the properties of the Er 2 O 3 films due to rapid thermal annealing processes in O 2 ambient performed at temperatures in the range 800–1200 °C has been investigated in details. The existence of well-defined annealing conditions (temperature of 1100 °C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. The same annealing processes are less effective when Er 2 O 3 is deposited on Si. In this latter case interfacial reactions and pit formation occur, leading to a material characterized by stronger non-radiative phenomena that limit the PL efficiency.

In this work we have studied the structural, electrical and optical properties of MOS devices, where the dielectric layer consists of a SiOx (x < 2) thin film prepared by plasma enhanced chemical vapor deposition and implanted with rare earth ions. As deposited SiOx films were annealed at high temperature (> 1000 degreesC) to induce the separation of the Si and SiO2 phases with the formation of Si nanocrystals embedded in the insulating matrix. Devices based on this system present a strong light emission at room temperature at a wavelength of about 900 nm. Devices emitting at different wavelengths have been fabricated by implanting SiOx films with Er or Tin. Devices based on Er-doped Si nanoclusters film exhibit an intense 1.54 mum room temperature electroluminescence (EL). We have calculated the excitation cross-section for Er ions in presence of Si nanoclusters under electrical pumping and the value is similar to1 x 10(-14) cm(2), comparable to the value found for the electrical excitation of undoped Si nanocrystals. Finally, devices based on Tm-doped Si nanoclusters exhibit two EL peaks at 0.78 and 1.7 mum.

In the present paper, we will review our recent work on Er-doped Si nanoclusters. We demonstrate that amorphous as well as crystalline Si clusters are efficient sensitizers for the Er 3+ luminescence at 1.54 μm. The samples have been obtained by implanting Er in a film containing pre-formed Si nanocrystals. After the implant, samples have been treated at 900 °C for 1 h, in order to activate Er 3+ . It is shown that this annealing temperature is not enough to re-crystallize all of the amorphized Si clusters. However, even if the Si nanoclusters are in the amorphous phase, they can still efficiently transfer the energy to nearby Er ions. We present a model based on an energy level scheme taking into account the coupling between each Si nanocluster and the neighboring Er ions. By fitting the data, we were able to determine a value of 3×10 −15 cm 3 s −1 for the Si nanocluster–Er coupling coefficient. Moreover, a strong cooperative up-conversion mechanism, active between two excited Er ions and characterized by a coefficient of 7×10 −17 cm 3 s −1 , will be shown to be active in the system, demonstrating that more than one Er ion can be excited by the same nanocluster. In addition, we found that the overall light emission yield of the Er related luminescence can be enhanced by using higher concentrations of very small nanoaggregates. Finally, room temperature operating electroluminescent devices based on Er-doped Si nanoclusters will be demonstrated.

Light emission in crystalline silicon (c-Si) has been a subject of intense research over the past two decades. Many different strategies have been explored to make silicon an efficient infrared emitter at strategic telecom wavelengths, including doping with rare-earth atoms, or exploiting optically active structural defects.

Bilayers consisting of two SiOC films doped with Eu at different concentrations have been synthesized by magnetron cosputtering. The proper choice of annealing temperature allows us to avoid Eu diffusion and clustering, so that each layer maintains its optical properties. Under these conditions, the bilayer allows us to take advantage of the dependence of the photoluminescence peak position on the Eu concentration, so that an intense white emission is obtained at room temperature. This finding constitutes relevant progress towards the realization of efficient Si-based white light sources, which can be of great interest for applications in photonics or solid-state lighting. (C) 2014 The Japan Society of Applied Physics

The influence of bismuth on erbium optical properties at 1.54 mu m has been investigated in yttrium-erbium disilicate thin films synthesized by magnetron co-sputtering and implanted with two Bi different doses. The Bi depth distribution and the evolution of its oxidation states after annealing treatments at 1000 degrees C in two atmospheres, O-2 and N-2, have been investigated. It was found that only in O-2 the Bi3+ valence state is prevalent, thanks to the enhanced Bi mobility in the oxidizing ambient, as demonstrated by Rutherford backscattering spectrometry. At lower Bi content, although the formation of Bi 0 metallic nanoparticles that are deleterious non radiative channels for Er luminescence, efficient energy transfer from Bi to Er has been obtained only in O-2. It is due to the excitation of ultraviolet broad Bi3+ absorption band and the energy transfer to Er ions. We have evaluated that in this case, Er effective excitation cross section increased by a factor of 5 in respect with the one for direct Er absorption at 488 nm. At higher Bi dose, this mechanism is absent, but an increased Er optical efficiency at 1.54 mu m has been observed under resonant excitation. It is due to the contribution of a fraction of Er ions having an increased lifetime. This phenomenon is associated with the formation of Bi agglomerates, induced at higher Bi doses, which well isolate Er from non-radiative quenching centers. The increased decay time assures higher optical efficiency at 1.54 mu m. (C) 2014 AIP Publishing LLC.

We report on the investigation of the structural, chemical and optical properties of undoped and Eu-doped SiOC thin films synthetized by RF magnetron sputtering. Undoped SiOC exhibits an intense room temperature luminescence at similar to 500 nm, and an important contribution to this signal is due to the presence of Si-C bonds. Moreover, when inserted in a SiOC matrix, Eu ions have a higher solid solubility with respect to pure SiO2; as a consequence, we observe a reduction of Eu clustering phenomena. Furthermore the reducing properties of SiOC, related to the presence of C, allow the prevalence of the Eu2+ emission over the Eu3+ one. Through the control of the annealing conditions it is possible to obtain an intense light emission at 440 nm. These properties propose SiOC as a novel and efficient Si-based host matrix for Eu and open the way to promising perspectives of Eu-based materials for photonic applications and LED fabrication.

A promising approach to obtain light emission from Si-based materials is represented by doping with rare earths and in particular with Eu. In this paper the comparison of the performances of SiO 2 and SiOC layers as host matrices for optically active Eu ions is presented. A SiO 2 matrix allows to observe light emission from both Eu 2+ and Eu 3+ ions, owing to a proper tuning of the thermal annealing process used to optically activate the rare earth. However the photoluminescence efficiency of both ions remains relatively low and quite far from the requirements for technological applications, mainly due to the extensive formation of Eu-containing precipitates. A detailed study of the structural and optical properties of these layers allowed us to analyze and elucidate the clustering process and to find suitable strategies to minimize it. We found that the substitution of the SiO 2 matrix with a SiOC film allows to obtain a very bright light emission at about 440 nm from Eu 2+ ions. In fact SiOC is able to efficiently promote the Eu reduction; furthermore, Eu ions are characterized by an enhanced mobility and solubility in this matrix and, as a consequence, Eu precipitation is strongly reduced. Finally, by taking advantage of the dependence of the photoluminescence peak position on the Eu concentration, an intense white emission is obtained at room temperature by combining two layers with different Eu contents. Since SiOC is a material fully compatible with standard Si technology, Eu-doped SiOC layers can be considered a highly interesting candidate for applications in photonics or in solid-state lighting.

The comparison of the performances of SiO2 and SiOC layers as host matrices for optically active Eu ions is presented. A SiO2 matrix allows to observe light emission from both Eu2+ and Eu3+ ions, owing to a proper tuning of the thermal annealing process used for the optical activation of the rare earth. However, the photoluminescence efficiency of both ions remains relatively low and quite far from the requirements for technological applications, mainly due to the extensive formation of Eu-containing precipitates. A detailed study by transmission electron microscopy allowed us to analyze and elucidate the clustering process and to find suitable strategies for minimizing it. We found that the substitution of SiO2 matrix with a SiOC film allows to obtain a very bright light emission centered at about 440 nm from Eu2+ ions. In fact, SiOC is able to efficiently promote the Eu3+ → Eu2+ reduction; furthermore, Eu ions are characterized by an enhanced mobility and solubility in this matrix, and as a consequence, Eu precipitation is strongly reduced. Since SiOC is a material fully compatible with standard Si technology, Eu-doped SiOC layers can be considered a highly interesting candidate for photonic applications.

In this work, we investigate the spectral response of metal-oxide- semiconductor photodetectors based on Ge nanoclusters (NCs) embedded in a silicon dioxide (SiO2) matrix. The role of Ge NC size and density on the spectral response was evaluated by comparing the performance of PDs based on either densely packed arrays of 2 nm-diameter NCs or a more sparse array of 8 nm-diameter Ge NCs. Our Ge NC photodetectors exhibit a high spectral responsivity in the 500-1000 nm range with internal quantum efficiency of ~ 700% at - 10 V, and with NC array parameters such as NC density and size playing a crucial role in the photoconductive gain and response time. We find that the configuration with a more dispersed array of NCs ensures a faster photoresponse, due to the larger fraction of electrically-active NCs and the partial suppression of recombination centers. The photoconduction mechanism, assisted by trapping of photo-generated holes in Ge NCs, is discussed for different excitation power and applied bias conditions. Our results provide guidelines for further optimization of high-efficiency Ge NC photodetectors. © 2013 Elsevier B.V. All rights reserved.

In this work, ultrathin amorphous Ge films (2 to 30 nm in thickness) embedded in SiO2 layers were grown by magnetron sputtering and employed as proficient light sensitizer in photodetector devices. A noteworthy modification of the visible photon absorption is evidenced due to quantum confinement effects which cause both a blueshift (from 0.8 to 1.8 eV) in the bandgap and an enhancement (up to three times) in the optical oscillator strength of confined carriers. The reported quantum confinement effects have been exploited to enhance light detection by Ge quantum wells, as demonstrated by photodetectors with an internal quantum efficiency of 70%. © 2013 Cosentino et al.

Highly Er-doped Yb-Y disilicates thin films grown on c-Si will be presented. The approach has permitted to vary independently the concentrations of both active rare earths, Er and Yb, and to effectively control the Er sensitization from Yb ions. We will demonstrate that these films are stable, having a uniform distribution of the chemical components throughout their thickness and a favored crystallization of the alpha-phase, which is the most optically efficient. We verified that this crystallization can be ascribed to a densification of the material and to the mobility locally introduced by ion implantation. Finally we will show a strong PL emission at 1.54 mu m, associated to the Yb-Er energy transfer mechanism, without any deleterious energy back-transfer. These properties make this new class of thin films a valuable and promising approach for the realization of efficient planar amplifiers. (C) 2012 Optical Society of America

The intense luminescence of SiOC layers is studied and its dependence on the parameters of the thermal annealing process elucidated. Although the emission of SiOC is bright enough to be interesting for practical applications, this material is even more promising as a host matrix for optically active Eu ions. Indeed, when incorporated in a SiOC matrix, Eu(3+) ions are efficiently reduced to Eu(2+), producing a very strong visible luminescence peaked at 440 nm. Eu(2+) ions benefit also of the occurrence of an energy transfer mechanism involving the matrix, which increases the efficiency of photon absorption for exciting wavelengths shorter than 300 nm. We evaluate that Eu doping of SiOC produces an enhancement of the luminescence intensity at 440 nm accounting for about a factor of 15. These properties open the way to new promising perspectives for the application of Eu-doped materials in photonic and lighting technologies.

We present the different approaches we recently followed to achieve intense room temperature photoluminescence (PL) from Si-based materials. On one side we obtained sub-bandgap PL from H-related defects induced by the H-2 plasma treatment of Si photonic crystal (PhC) nanocavities. We demonstrated that a strong and narrow PL emission can be obtained in the PhC nanocavities due to the formation of a damaged layer mainly consisting of nanometric platelets and bubbles. An overall 40000-fold enhancement of the PL signal, with respect to pure crystalline Si, has been achieved and moreover the signal can be tuned in a wide range by only changing the PhC parameters. On the other side, we focused our attention on the properties of SiO2 and SiOC host matrices doped with Eu ions. C addition produces a strong enhancement of the Eu PL with respect to pure SiO2 films. The chemical and structural characterization of these materials reveals an extensive Eu clustering in SiO2-based films, while C addition induces a significant reduction of this phenomenon, enhancing the fraction of optically active Eu ions. These results can be applied for the realization of efficient Si-based light sources.

Europium-based materials are known for their intense and stable emission in the visible region. Moreover Eu is stable in both its divalent and trivalent oxidation states. In particular, emission of Eu2+ is much stronger, being allowed for electric dipole transition rules and is characterized by a broad peak, centered in the wavelength range 400–600 nm, while that of Eu3+ presents several sharp lines at around 600 nm. These peculiar optical properties make Eu‐based systems an interesting material for photonic applications. The optical and structural properties of Eu2O3 thin films grown by RF magnetron sputtering on Si substrates have been studied. PL emission has been observed at room temperature and it is strongly dependent on the thermal process. In particular, annealing in O2 atmosphere leads to an enhancement of the Eu3+ emission, while films annealed in N2 ambient exhibit a very intense PL signal due to Eu2+. The chemical and structural characterization of the films, performed by TEM and XPS, reveals that a massive mixing at the Eu2O3‐Si interface occurs in N2‐annealed samples, leading to the formation of Eu (II) silicates, while in the case of O2-annealed samples we observe the formation of a SiOx layer at the interface, that minimize the diffusion of Si into the Eu2O3 layer.