A. Creti

INO - Istituto Nazionale di Ottica, Florens, Tuscany, Italy

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Publications (29)63.47 Total impact

  • Sandro Lattante · arianna cretì · mauro lomascolo · marco anni
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    ABSTRACT: We investigate the Amplified Spontaneous Emission (ASE) properties of a prototypical host-guest polymer polymer blend, namely poly(9,9-dioctylfluorene) (PF8) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) blend, with different concentration ratio. We show that the initial F8BT content increase causes an increase of the F8BT ASE threshold, even leading to ASE suppression for F8BT contents between 25% and 75%. ASE is then recovered upon further increase of the F8BT relative content. We demonstrate that the ASE properties of the PF8:F8BT are dominated by morphology effects, like submicrometric phase segregation, determining the net gain of the active waveguides.
    No preview · Article · Feb 2016 · Organic Electronics
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    ABSTRACT: A promising new generation of solar thermal collector able to enhance the thermal efficiency is the DASC (Direct Absorber Solar Collector). In this paper we report optical absorption measurements performed on several water-based nanofluids (Al2O3, CuO, TiO2, ZnO, CeO2, and Fe2O3) as a function of nanoparticles concentration. These measurements are of fundamental importance to assess the possibility to use the above mentioned metal-oxide nanoparticles in liquid-based nanofluids for direct absorption low temperature flat panel solar collector. The obtained results show different optical behaviors of the nanofluids depending on nanoparticles material and concentration. In all measurements the transmittance rises passing from visible to infrared region and in some cases, when the nanoparticles concentration is too low, the extinction distance grows up to values larger than the typical diameter of a solar receiver.
    Full-text · Article · Jan 2016 · Solar Energy Materials and Solar Cells
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    ABSTRACT: The use of nanofluids as working fluids in direct absorption solar collector is growing up and the study of optical properties of nanoparticles is an important step for the success of this new technology.In this paper we report optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, and Fe2O3) as a function of temperature in the range 25-500°C, in order to study their optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in Concentrated Solar Power (CSP).
    No preview · Article · Jan 2015 · Solar Energy Materials and Solar Cells
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    ABSTRACT: In this work two quantum dot (QD) solar cell structures have been proposed and compared as potential solutions for the realization of the Intermediate Band Solar Cell concept: the well known dot/barrier material system InAs / GaAs and an engineered InAlGaAs/AlGaAs combination. The Al-based structures have been obtained by a suitably developed growth procedure with the aim of increasing island density and engineering the absorption spectrum and the energy band profile in the near infrared region. Along with tunability of the confined electron energy levels, the proposed Al-based structures exhibit transport features, such as reduced edge recombination losses and lower reverse saturation current density with respect to the InAs/GaAs QD system, which can be useful for enhancing device performances.
    No preview · Conference Paper · May 2014
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    ABSTRACT: In this paper we report on optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, Fe2O3) as a function of temperature in the range 25500 °C, in order to study the optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in concentrated solar power (CSP).
    No preview · Article · Sep 2013

  • No preview · Conference Paper · Jan 2013
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    ABSTRACT: The optical response by NO2 gas adsorption at different concentrations has been investigated, at room temperature, in ZnO nanostructured films grown by controlled vapor phase deposition. The variation (quenching) in the photoluminescence signal from excitonic and defects bands, due to the interactions between the oxidizing gas molecules and the sample surface, has been detected and dynamic responses and calibration curves as a function of gas concentration have been obtained and analyzed for each band. We showed that the sensing response results larger in excitonic band than in defect one and that the emission signal rises from two different quenchable and unquenchable states. A simple model was proposed in order to explain the quenching processes on the emission intensity and to correlate them to the morphological features of the samples. Finally, the reversibility of the quenching effects has also been tested at high gas concentration.
    Full-text · Article · Apr 2012 · Journal of Applied Physics

  • No preview · Chapter · Mar 2012
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    ABSTRACT: We have investigated the optical properties of colloidal seed-grown CdSe (seed)/CdTe (arms) nanotetrapods both experimentally and computationally. The tetrapods exhibit a type-II transition arising from electrons localized in the CdSe seed region and holes delocalized in the CdTe arms, along with a residual type-I recombination in long-arm tetrapods. Experiments and theory helped to identify the origin of both types of transitions and their size dependence. In particular, time-resolved experiments performed at 10 K evidenced a size-dependent, long living type-II radiative emission arising from the peculiar electron–hole wave function localization. Temperature-dependent photoluminescence (PL) studies indicate that, at high temperature (>150 K), the main process limiting the PL quantum efficiency of the type-I PL is thermal escape of the charge carriers through efficient exciton-optical phonon coupling. The type-II PL instead is limited both by thermal escape and by the promotion of electrons from the conduction band of the seed region to that of the arms, occurring at T > 200 K.
    No preview · Article · Aug 2011 · The Journal of Physical Chemistry C
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    ABSTRACT: Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700°C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO2. The variation in the photoluminescence emission of the films when exposed to NO2 was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO2 concentrations down to 3 ppm at room temperature.
    Full-text · Article · Mar 2011 · Laser Physics
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    ABSTRACT: This chapter aims to present a brief review about a very interesting application of laser beams in the field of materials science: the growth of zinc oxide (ZnO) nanostructured films by Pulsed Laser Deposition (PLD), and in particular by means of excimer laser ablation. After an introduction giving an overview on properties and applications of ZnO and its nanostructures and on some growth techniques used to obtain these materials, this survey will present several results, obtained by different research groups in the world, about nanostructured ZnO grown by excimer laser ablation. Then this study will be focused on the results obtained by our research group in this field so far. By properly changing some deposition parameters (substrate temperature, oxygen pressure and ablation laser wavelength) we obtained nanostructured films with hexagonal pyramids, columns, hexagonal hierarchical structures and pencils, as well as smooth or rough films. In particular the different ablation laser wavelengths (248 nm of KrF and 193 nm of ArF) are shown to have a deep influence on both morphology and crystal quality of the grown samples. Scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL) measurements were used to inspect the film properties. Finally, some results about our optical gas sensing tests conducted on the grown samples are presented.
    No preview · Chapter · Jan 2011
  • A. Cretí · M. Lomascolo
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    ABSTRACT: In this chapter we focus on the exciton relaxation dynamics of colloidal CdSe core and core/shell nanorods. In particular we show how confinement effects and defect states affect linear and non linear optical properties. We present a brief introduction on the colloidal nanocrystals (NCs), namely on their electronic and optical properties, and on the recombination processes in these materials. Then we discuss the results of our systematic study of ultrafast exciton relaxation dynamics in CdSe core and CdSe/CdS/ZnS core/shell nanorods with a radius of few nm, different length (20-40 nm) and different shell thickness. Femtosecond pump-probe spectroscopy, in the visible spectral range with non resonant / resonant pump energy has been performed to investigate the fast processes in NCs. The effect of the shell thickness on Stimulated Emission (SE) and Photoinduced Absorption (PA) transitions in core and core/shell CdSe nanorods is exposed and the role of surface/interface defect states is pointed out. We show that the defect states distribution depends on the shell thickness and that the interface defects can be negligible for thin ones, resulting in a longer lifetime of SE. Furthermore we demonstrate that a resonant pumping increases the SE lifetime and enhances Auger scattering, clarifying that PA processes, involving defect states, are the main obstacle to sustain the SE. In the case of resonant pumping measurements the role of defect states on Auger processes and the presence of coherent confined acoustic phonons in CdSe core nanorods are also discussed. In particular we find that the modulation frequency observed in photobleaching and photoabsorption dynamics of core NCs, corresponds to the coherent radial breathing modes of the nanorods. Finally we quantitatively investigate, by time resolved photoluminescence (PL) spectroscopy, the shell thickness dependence of exciton trapping and its effects on the PL quantum yield.
    No preview · Article · Jan 2011
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    ABSTRACT: Matrix-assisted pulsed laser evaporation (MAPLE) was used to deposit layers of poly(9,9-dioctylfluorene) (PFO) to study the relation between the solvent properties (laser light absorption, boiling temperature and solubility parameters) and the morphology of the deposited films. To this end, the polymer was diluted (0.5 wt%) in tetrahydrofuran—THF, toluene and toluene/hexane mixtures. The thickness of the films was equal to 70±20 nm. The morphology and uniformity of the films was investigated by Atomic Force Microscopy and by the photoluminescence emission properties of the polymer films, respectively. It is shown that, although the solubility parameters of the solvents are important in controlling the film roughness and morphology, the optical absorption properties and boiling temperature play a very important role, too. In fact, for matrices characterized by the same total solubility parameter, lower roughness values are obtained for films prepared using solvents with lower penetration depth of the laser radiation and higher boiling temperatures.
    No preview · Article · Dec 2010 · Applied Physics A
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    ABSTRACT: In this work, the evolution of the Au assisted-growth of ZnO nanorods deposited by vapour phase deposition both on sapphire and on indium–tin–oxide on glass (ITO-glass) substrates has been studied. Our investigation demonstrates that the growth proceeds first as a 3D growth, giving rise to a buffer layer, few microns thick, formed by ZnO grains with different orientation. Then a 1D transition occurs with the nucleation of a dense array of vertically aligned nanorods. A different degree of crystalline order and nanorods alignment was found between the samples grown on ITO-glass and sapphire substrates, which was ascribed to the different morphology that the Au seed layer acquires on the two different substrates. A semi-quantitative analysis of the ZnO crystalline orientation was carried out by X-ray diffraction (XRD) measurements performed at fixed incidence configuration and supported by high resolution scanning electron microscopy (HR-SEM) investigations on focused ion beam (FIB) prepared cross-sections.
    Full-text · Article · Sep 2010 · Materials Science and Engineering B
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    ABSTRACT: We report on nitrogen dioxide (NO2) sensing measurements by means of zinc oxide films presenting different morphologies. The variation in the photoluminescence emission of the films is employed as transduction mechanism to detect the presence of NO2 gas molecules at room temperature. The significant role of film morphology on the sensing properties is presented and possible limits in the use of ZnO nanostructures for NO2 detection at high gas concentration (>20 ppm) and low gas flow (50 ml/min), where a worsening of the sensor response is observed, are discussed. These features are ascribed to a likely incomplete reversibility of the NO2 adsorption process and examined in connection with the mechanisms of interaction between NO2 molecules and ZnO.
    No preview · Article · Mar 2010 · Sensors and Actuators B Chemical
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    ABSTRACT: We investigated the excitation density dependence of the photoluminescence spectra of hybrid poly(9,9-dioctylfluorene)-CdSe/ZnS nanocrystals (PF8-NCs) thin films. We demonstrate that this experiment allows the determination of the efficiency of all the CdSe/ZnS NCs excitation processes and that the presence of amplified spontaneous emission (ASE) from the PF8 leads to a strong dependence of the NC excitation processes from the laser excitation density. Below the PF8 ASE threshold only about 6% of the excitons in the NCs are due to pump laser absorption, while about 94% of the NC excitation is due to the interaction with the PF8, and it is due for about 58% to PF8-->NC Forster resonant energy transfer (FRET) and for about 37% to reabsorption by the NCs of the PF8 luminescence. The presence of PF8 ASE significantly modifies this scenario by strongly decreasing the FRET importance and strongly increasing the reabsorption one. The interplay between reduced FRET and increased reabsorption overall decreases the NC excitation due to PF8 indicating that ASE from the donors should be avoided if efficient NCs excitation under strong pumping is wished.
    No preview · Article · Feb 2010 · The Journal of Physical Chemistry A

  • No preview · Chapter · Jan 2010
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    ABSTRACT: Zinc oxide (ZnO), particularly in its nanostructured forms, is one of the materials extensively studied in the last years due to the great number of its possible applications. Several growth techniques can be used to realize this kind of material and, among them, the Pulsed Laser Deposition (PLD) technique has been demonstrated to be a very versatile method to easily control the properties of the grown material.In this regard, this book aims to presents a review about the growth of zinc oxide (ZnO) nanostructured films by Pulsed Laser Deposition (PLD), and in particular by means of excimer laser ablation.
    No preview · Book · Jan 2010
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    ABSTRACT: Zinc oxide films with different morphologies have been grown by pulsed laser deposition, varying substrate temperature and oxygen pressure. At low oxygen pressure and low substrate temperature continuous films with different roughness have been obtained, while at high substrate temperature a film with sparse hexagonal pyramids has been observed. Increasing the oxygen pressure the film became rougher and at 100 Pa a rod-array has been deposited. The columns of this rod-array grew along the wurtzite c-axis perpendicularly to the substrate surface as proved by X-ray diffraction measurements. Near to the sample borders the columns were slightly tilted towards the center of the sample. The possible growth mechanisms giving rise to the different morphologies have been discussed. Low-temperature photoluminescence measurements allowed to get information about the film quality, showing the variations of the excitonic peak and two defect bands (green and violet-blue) with the different deposition parameters.
    No preview · Article · Sep 2009 · Applied Surface Science
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    ABSTRACT: The optical response at room temperature of ZnO nanostructures, grown by controlled vapour phase deposition, to low concentrations of NO<sub>2</sub> gas mixed in dry-air has been investigated. In particular the quenching in the emission signal, due to the interactions between oxidizing gas molecules and sample surface, has been monitored in excitonic and defect band, as a function of NO<sub>2</sub> gas concentration. The dynamic responses and the resulting calibration curves, obtained for each emission band, have been compared. Furthermore responses of nanorods with different size and nanostructures with different exotic shape have been discussed in order to clarify the role of the morphology and/or dimensions and structural quality. In particular we have correlated the growth conditions and the resulting structural and optical properties of the samples, highlighting their role in the optical sensing response.
    Full-text · Conference Paper · Nov 2008

Publication Stats

479 Citations
63.47 Total Impact Points

Institutions

  • 2008-2012
    • INO - Istituto Nazionale di Ottica
      Florens, Tuscany, Italy
  • 2011
    • Istituto Italiano di Tecnologia
      Genova, Liguria, Italy
  • 2006
    • Politecnico di Milano
      • Department of Physics
      Milano, Lombardy, Italy
  • 2003
    • Università del Salento
      • Department of Engineering for Innovation
      Lecce, Apulia, Italy