Catia Clementi
University of Perugia
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Publication
Featured researches published by Catia Clementi.
Chemical Communications | 2009
Gianluca Accorsi; Giovanni Verri; Margherita Bolognesi; Nicola Armaroli; Catia Clementi; Costanza Miliani; A. Romani
Cuprorivaite (CaCuSi(4)O(10), also known as Egyptian blue) exhibits an exceptionally high emission quantum efficiency in the near-infrared region (lambda(max) = 910 nm, Phi(EM) = 10.5%) and a long excited state lifetime (107 mus); these properties make it appealing for several applications in the fields of biomedical analysis, telecommunications and lasers.
Journal of Physical Chemistry A | 2009
Anna Amat; Catia Clementi; Filippo De Angelis; Antonio Sgamellotti; Simona Fantacci
The absorption and emission properties of the two components of the yellow color extracted from weld (Reseda luteola L.), apigenin and luteolin, have been extensively investigated by means of DFT and TDDFT calculations. Our calculations reproduce the absorption spectra of both flavonoids in good agreement with the experimental data and allow us to assign the transitions giving rise to the main spectral features. For apigenin, we have also computed the electronic spectrum of the monodeprotonated species, providing a rationale for the red-shift of the experimental spectrum with increasing pH. The fluorescence emission of both apigenin and luteolin has then been investigated. Excited-state TDDFT geometry optimizations have highlighted an excited-state intramolecular proton transfer (ESIPT) from the 5-hydroxyl to the 4-carbonyl oxygen of the substituted benzopyrone moiety. By computing the potential energy curves at the ground and excited states as a function of an approximate proton transfer coordinate for apigenin, we have been able to trace an ESIPT pathway and thus explain the double emission observed experimentally.
Applied Spectroscopy | 2009
Catia Clementi; Costanza Miliani; Giovanni Verri; Sophia Sotiropoulou; A. Romani; Brunetto Giovanni Brunetti; Antonio Sgamellotti
The variations of the fluorescence emission of carmine lake travelling through an absorbing and scattering medium, such as a paint layer, were investigated by ultraviolet (UV)–visible absorption, fluorescence spectroscopy, and imaging techniques. Samples of the lake were studied in dilute and saturated solutions, on a reference test panel and a real case study. Relevant spectral modifications have been observed as a function of the lake concentration mainly consisting of a fluorescence quenching, red shift of emission maxima, and deformation of emission band. The application of a correction factor based on the Kubelka–Munk model allowed fluorescence spectra obtained in solution and on painted samples of known composition to be compared and correlated, highlighting that the fluorescence of the lake within paint layers is affected by both self-absorption and aggregation phenomena. This approach has been successfully applied on a painting by G. Vasari for the noninvasive identification of carmine lake. The results reported here emphasize the necessity of taking physical phenomena into account in the interpretation of the fluorescence spectra for a proper and reliable characterization and identification of painting materials in works of art.
Applied Spectroscopy | 2008
A. Romani; Catia Clementi; Costanza Miliani; Brunetto Giovanni Brunetti; Antonio Sgamellotti; G. Favaro
The prototype of a portable instrument, based on the time-correlated single-photon counting method, purposely assembled for in situ measurements of luminescence lifetimes on artwork surfaces, is here presented. Preliminary tests have been carried out using the portable instrument and the results have been compared with those obtained using a bench instrument. In this way we have proven that the prototype provides lifetime measurements with good precision. It is also shown that fluorescence lifetime determinations, coupled with steady-state fluorescence spectra, allow the distinguishing, on laboratory samples, of different red organic lakes having similar fluorescence spectra, achieving new boundaries in the nondestructive diagnosis of artwork materials. The first in situ application of the technique on an original work of art, The Book of Kells, held at Trinity College Library, Dublin, highlighted the diagnostic potential of coupled steady-state and time-resolved luminescence spectroscopy in the identification of organic colorants.
Applied Spectroscopy | 2008
Giovanni Verri; Catia Clementi; Daniela Comelli; Sharon Cather; Francesca Piqué
Ultraviolet-induced fluorescence spectroscopy is a commonly used technique for the characterization and identification of painting materials, such as organic binders and colorants. Its interpretation is strictly connected to both the experimental setup and an understanding of the physical and chemical interactions among materials in paint layers, which are commonly composed of a fluorescent organic binder and a pigment. When irradiated with ultraviolet radiation, the light emitted by fluorophores present in the organic binder undergoes several types of interactions, in particular scattering and absorption by neighboring pigmented particles and auto-absorption. As a result of scattering and absorption phenomena, the emission spectrum is deformed according to the physical properties of the surrounding pigmented particles. This can lead to shifts of the emission maxima and/or to the formation of apparent new emission bands. The extent of the modifications to the emission spectra, caused by auto-absorption and selective absorption phenomena, may lead to the erroneous characterization or identification of the fluorescent materials. As a consequence, the interpretation of the emission signal can be greatly compromised. A correction based on the Kubelka–Munk theory is proposed to evaluate the extent of the spectral distortion and is assessed on modern replicas of wall paintings of known composition. Although the model cannot be applied to all cases, qualitative distinctions between real and apparent emissions are achieved.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2009
Catia Clementi; Costanza Miliani; A. Romani; U. Santamaria; F. Morresi; K. Mlynarska; Gianna Favaro
In this paper, three Renaissance tapestries depicting scenes painted by Raffaello Sanzio, conserved at the Vatican Museum, were investigated using in-situ UV-Visible fluorimetric measurements. The results show that this technique is suitable for the detection of natural organic colorants used for dyeing the threads woven in these tapestries. The emission signals detected on red-purple colours were assigned to the colorant orcein and those on different nuances of blue and green colours to indigo by comparison with data from reference laboratory samples. The assignments were supported by chromatographic experiments carried out on threads taken from the back side of the tapestry in the same points analysed by spectrofluorimentry.
Applied Spectroscopy | 2012
Catia Clementi; Francesca Rosi; A. Romani; Riccardo Vivani; Brunetto Giovanni Brunetti; Costanza Miliani
Zinc oxide has been widely used as a white artist pigment since the end of the eighteenth century. The luminescence properties of this compound have received great interest during the last decades for promising applications in different fields of material science, but their diagnostic implications in the cultural-heritage context have been poorly exploited. This paper is intended to provide a clear picture of the luminescence behavior of zinc white in oil paintings. With this aim, three white pigments and three highly pure (analytical grade) zinc oxides were studied as powder substrates and as painting models by ultraviolet–visible (UV–VIS) fluorescence and Fourier transform infrared (FT-IR) spectroscopy. The quenching of the luminescence intensity of the UV excitonic emission due to self-absorption and multiple scattering phenomena has been investigated, pointing out the possible difficulty of detecting this signal with negative consequences in the diagnostics of works of art. By contrast, the UV emission is notably enhanced by interaction with the binder, whereas the visible emission decreases. This phenomenon is probably due to the formation of covalent bonds between zinc atoms and carboxylates from the lipidic medium that are chemisorbed on zinc oxide surfaces.
Photochemical and Photobiological Sciences | 2011
Chiara Grazia; Catia Clementi; Costanza Miliani; A. Romani
The present study was undertaken to investigate the photophysical properties of the organic-metal compounds which are the main components of madder lake, one of the most commonly used and widespread organic pigments in painted artworks, from both geographic and historic points of view. Alizarin- and purpurin-Al(III) complexes were studied in solution and as powders. In solution, the chelate stoichiometry, their absorption and emission properties and the efficiency of their excited electronic state deactivation pathways have been determined. The two organic-metal compounds show relevant differences in terms of spectral features consisting of multiple peak (structured) absorption and emission spectra for the purpurin derivative and single broad bands (structureless) for the Al(III)-alizarin chelate. For both the investigated molecules, the chelation process induces a relevant increase of the emission quantum yields and lifetimes. The main differences between photophysical properties of the two metal complexes concern emission quantum yield and lifetime, which are both higher for purpurin chelate compared to alizarine chelate. Furthermore, interesting differences between the two metal complexes concerning the relative relevance of inter- and intra-molecular interaction involved in the mechanism of the excitation energy dissipation have been also highlighted. The knowledge of the determined parameters allows better understanding of the spectral behaviour in the solid state, thus providing a solid reference for the non-invasive characterisation and identification of madder lake on original artworks through its absorption and emission features.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2013
Brenda Doherty; Alessia Daveri; Catia Clementi; A. Romani; Susan Bioletti; Brunetto Giovanni Brunetti; Antonio Sgamellotti; Costanza Miliani
This paper highlights the efficacy of non-invasive portable spectroscopy for assessing the execution technique and constituent materials in one of the most important medieval manuscripts, the Book of Kells. An aimed campaign of in situ measurements by the MObile LABoratory (MOLAB) has analyzed its elemental composition and vibrational and electronic molecular properties. The ample analytical toolbox has afforded complementary diagnostic information of the pigment palette permitting the characterization of both inorganic and organic materials as pigments and dyes in the white, purple, blue, red, orange, green and black areas. In particular, the novel widespread use of calcinated gypsum (anhydrite) as both a white pigment and in correlation to the organic dyes in this manuscript has been noted. The non-invasive identification of the organic dye orchil is significant considering its rare non invasive detection in medieval manuscripts. Finally the occurrence of particular alterations of the organic black areas giving rise to calcium carboxylate and calcium oxalate has been specifically highlighted. Importantly, this work elaborates complex aspects of the employed painting materials which have given rise to numerous significant points of interest for a more elaborate understanding of this Irish treasure.
Analytical and Bioanalytical Chemistry | 2011
Catia Clementi; Valeria Ciocan; Manuela Vagnini; Brenda Doherty; Marisa Laurenzi Tabasso; Cinzia Conti; Brunetto Giovanni Brunetti; Costanza Miliani
The paper reports on the exploitation of an educated multi-technique analytical approach based on a wide non invasive step followed by a focused micro-destructive step, aimed at the minimally invasive identification of the pigments decorating the ceiling of the Gilded Vault of the Domus Aurea in Rome. The combination of elemental analysis with molecular characterization provided by X-ray fluorescence and UV–vis spectroscopies, respectively, allowed for the in situ non-invasive identification of a remarkable number of pigments, namely Egyptian blue, green earth, cinnabar, red ochre and an anthraquinonic lake. The study was completed with the Raman analysis of two bulk samples, in particular, SERS measurements allowed for the speciation of the anthraquinonic pigment. Elemental mapping by scanning electron microscopy-energy dispersive spectrometer combined with micro-fluorimetry on cross-section gave an insight into both the distribution of different blend of pigments and on the nature of the inorganic support of the red dye.