The study of cultural heritage can take advantage of modern non-destructive analysis technique ab... more The study of cultural heritage can take advantage of modern non-destructive analysis technique able to identify, among the others, the composition of the investigated ancient artifacts. In the present paper we applied Raman spectroscopy to analyze selected Mesopotamian materials from Kish kept in the Ashmolean Museum of the University of Oxford to investigate the pottery technique of that ancient people, with particular reference to the painting procedure. Beside the use of hematite and gypsum as red and white pigment respectively, the use of a near infrared laser excitation allowed to detect the presence of specific compounds applied at the pottery surface. Residual traces of the used oil were detected thanks to the fingerprint vibration at 1870 cm- 1 which is ascribed to the C=C stretching of the cyclopropenoid compound of some fatty acids and, in particular, assignable to the use of oils derived by sterculiaceae and malvaceae plants. By using DFT calculations we simulated the degradation process of the hypothesized initial oil and we propose the attribution of the final compound revealed by Raman analysis. From the reported experimental results we propose that the oil was applied all over the surface of the pottery as a primer before the painting decoration with the use of the dry oil technique.
Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy a... more Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy and EDAX measurements. The analysis of the Raman spectra of the surfaces reveals the presence calcium hydroxide (peak at about 780 cm−1) while the calcium carbonate is totally absent. The comparative studies on the carbonation effect of the surfaces were performed on laboratory grown samples of calcium hydroxide. The samples were treated at high temperature and exposed to different ambient conditions, and the analysis suggests that the original surfaces of Roman pottery were scattered by calcium hydroxide (limewash) before the cooking
process in the furnace. The result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce the content of CO2 in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the pottery. These results give new insights on the real degree of knowledge of the Romans about the art of ceramics and more generally about chemistry and technologies.
The light-induced phase transition of TiO2 nanoparticles from anatase to rutile structure is repo... more The light-induced phase transition of TiO2 nanoparticles from anatase to rutile structure is reported depending on the surrounding environment, the transition being accomplished under oxygen-poor conditions. The transition mechanism is interpreted in the framework of oxygen adsorption and desorption phenomena with the involvement of surface oxygen vacancies and F centers. It is shown that the observed phase transition is not thermally driven because the local temperature of the nanoparticles during irradiation is about 370 K (estimated through the Stokes to anti-Stokes Raman peaks ratio). On the contrary, the phase transition is initiated by intragap irradiation (with the exception of the red light one) that acts as TiO2 surface sensitizer, promoting the activation of the surface and the nucleation of rutile crystallites starting from two activated anatase neighboring nanoparticles.
The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support ... more The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support and dissolved in distilled water solution are compared with the optical properties of the dye dissolved in ethanol and discussed on the basis of the formation of different chemical species of the dye molecule. The presence of the polymeric support affects both the absorption and emission features of the coumarin by changing the chemical equilibrium among the different species typically observed at the ground and excited states. The optical properties of synthesized PEG-supported coumarins are able to warrant biomedical applications in water-based environment and enable us to gain insight into the photophysical activity of coumarins; in particular, the steric hindrance of the polymeric support inhibits, as expected, the formation of the tautomeric form of the compound in the excited state, a further proof of the single-step neutral to tautomer reaction in coumarins.
Mixed tin–iridium oxide (Sn0.85Ir0.15O2) nanoparticles at low Ir content (15 mol%) were prepared ... more Mixed tin–iridium oxide (Sn0.85Ir0.15O2) nanoparticles at low Ir content (15 mol%) were prepared by the sol–gel preparative route, varying calcination temperatures in the range 450–550 °C. The crystal structures, the phase composition and crystallite sizes were analyzed by X-ray powder diffraction (XRD). The local order of the materials was investigated by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) analysis revealed the variation of the Ir surface state with the temperature of firing. The morphology of crystallites and the aggregates were analyzed by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM), respectively. Nitrogen physisorption by BET method was adopted to evaluate the particle surface area and the mesopore volume distribution. Electrochemical properties of the Ti-supported powders were evaluated by cyclic voltammetry (CV) and quasi steady-state voltammetry.
High-resolution photoluminescence spectra of Fe:YAG crystals were recorded in the temperature ran... more High-resolution photoluminescence spectra of Fe:YAG crystals were recorded in the temperature range 10-150 K with different excitation energies, ranging from the band gap energy (6.88 eV) down to selective excitation of Fe(3+) ions (2.40 eV). Iron levels fine structure is found in the zero phonon lines, whose characteristics hint at the presence of the doping Fe(3+) ion in the tetrahedral site with a dynamic Jahn-Teller effect inherent in the (4)T(1) excited states. The analysis of the zero phonon interactions with acoustic phonons was achieved through linear and quadratic electron-phonon coupling models, and the Huang-Rhys factor, the Debye temperature, and the electron-phonon coupling were calculated in the framework of the Debye approximation by including only the Raman two-phonon process. The interactions with lattice phonons were studied, and the results were found to be correspondent to the expected results from previous vibrational data.
Proposed herein is a method based on the Levenberg–Marquadt technique to retrieve an approximated... more Proposed herein is a method based on the Levenberg–Marquadt technique to retrieve an approximated average phonon dispersion curve from Raman spectra of nano-sized crystals. To this end we deal with a modified form of the well-known phonon confinement model in which the intrinsic linewidth Γ0 is replaced by an effective linewidth Γ. An application to experimental results obtained on TiO2
The mechanisms of porous gallium phosphide formation by anodic etching are studied. Gallium phosp... more The mechanisms of porous gallium phosphide formation by anodic etching are studied. Gallium phosphide porous samples <100> oriented were prepared in sulfuric acid solution with different concentrations of NaF. The current-voltage characteristic curve depends on the NaF concentrations and shows the typical behavior for porous semiconductors formation. Four regions can be distinguished in the I-V curve: a pore formation zone, a dielectric layer growth, a transition region in which the two processes compete for the control of the surface morphology and finally the GaP surface electropolishing. The oxide formation shifts to higher potential and the pore formation zone is widened by adding fluorides in the etching solution. Raman spectroscopy is applied to investigate the surface morphology of samples prepared in different anodizing current density conditions and in different acid solutions. As regards the dielectric growth, the direct observation of the sample surface and the analysis of the vibrational spectra indicate that in different potential regimes two chemically different oxides can be formed.
Physica Status Solidi A-applications and Materials Science, 2010
Monocrystal matrices of high-gap oxides are finding increasing applications as hosts of luminesce... more Monocrystal matrices of high-gap oxides are finding increasing applications as hosts of luminescent ions, typically rare earths (RE)s. Currently, RE-doped oxyorthosilicates, aluminum perovskites, and garnets (RE2SiO5–REAlO3–RE3Al5O12) are widely used as highly efficient and fast scintillators for γ-ray detection. On the other hand, shallow or deep intragap energy levels, due to stoichiometric deviation or impurities unintentionally added in the crystals, play a counteractive role giving rise to slower scintillation decay time, reduced light yield and afterglow. The aim of this work is to show how it is possible to tailor these unwelcome outcomes and RE-ion interactions for engineering new devices for optical memory storage. In this sense, experimental results of thermo- and radio-luminescence are presented. The role of the bandgap and the location in energy of the levels due to the RE dopants and to the defects is discussed from a theoretical point of view. The feasibility in the near future of new promising transparent displays is also discussed.
This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr... more This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr(3+) ions in an yttrium aluminium garnet (YAG) matrix. Experimental data were analysed in the framework of electron-phonon coupling in the quadratic approximation and it was found that Cr(3+) ions in the YAG matrix are strongly coupled with lattice vibrations, with a Debye temperature of about 550 K and a value of the quadratic coupling constant of 0.65. The analysis of both homogeneous and inhomogeneous contributions to the photoluminescence linewidth is performed and the results obtained are compared with previously reported data for Fe(3+):YAG and discussed with respect to the different dependences of the two transition metal ions on the crystal field.
ABSTRACT In this paper, we report the anatase-to-amorphous phase conversion of TiO2 nanoparticles... more ABSTRACT In this paper, we report the anatase-to-amorphous phase conversion of TiO2 nanoparticles by means of low intensity visible light excitation. A proper choice of power density of the incident radiation and of partial pressure of oxygen in the experimental room allows a local and precise control on the phase of TiO2 nanoparticles. The 2.54 eV light of an Ar+ laser was used to induce structural changes on the samples and to collect photoluminescence spectra, while the 1.96 eV light of a He−Ne laser was utilized for in situ Raman measurements to give immediate proof of the crystallographic structure of the samples. In opposition to other light induced processes, based on the temperature effect, the phase conversion is due to surface modifications by a proper depletion of adsorbed oxygen on the crystal surface.
Mechanically activated anatase powders were used to assemble thin film electrodes for electrophot... more Mechanically activated anatase powders were used to assemble thin film electrodes for electrophotocatalytic applications. Flat band potential of the different samples, estimated from the dependence of photopotential on the light intensity, as well as photocurrent vs potential curves were measured at samples milled for different times and compared with those of the untreated anatase. The maximum performance is achieved at
The structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO3) were inv... more The structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO3) were investigated by means of Raman spectroscopy and EXAFS measurements.The analysis of Raman spectra taken in four different polarized configurations along the principal axes at 20K and room temperature conditions permits to assign the principal vibrational modes in LuAP single crystals and to confirm the belonging to the D2h16 space group.EXAFS measurements were performed at room temperature in order to obtain local structural informations on the first and next nearest neighbors around lutetium absorptions sites. Unit cell parameters and bond lengths were determined by the analysis of the EXAFS spectroscopy at the L3 absorption edge of lutetium.The informations thus gathered on this compound can offer a useful addition in the framework of a full structural characterization of LuAlO3.
The study of cultural heritage can take advantage of modern non-destructive analysis technique ab... more The study of cultural heritage can take advantage of modern non-destructive analysis technique able to identify, among the others, the composition of the investigated ancient artifacts. In the present paper we applied Raman spectroscopy to analyze selected Mesopotamian materials from Kish kept in the Ashmolean Museum of the University of Oxford to investigate the pottery technique of that ancient people, with particular reference to the painting procedure. Beside the use of hematite and gypsum as red and white pigment respectively, the use of a near infrared laser excitation allowed to detect the presence of specific compounds applied at the pottery surface. Residual traces of the used oil were detected thanks to the fingerprint vibration at 1870 cm- 1 which is ascribed to the C=C stretching of the cyclopropenoid compound of some fatty acids and, in particular, assignable to the use of oils derived by sterculiaceae and malvaceae plants. By using DFT calculations we simulated the degradation process of the hypothesized initial oil and we propose the attribution of the final compound revealed by Raman analysis. From the reported experimental results we propose that the oil was applied all over the surface of the pottery as a primer before the painting decoration with the use of the dry oil technique.
Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy a... more Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy and EDAX measurements. The analysis of the Raman spectra of the surfaces reveals the presence calcium hydroxide (peak at about 780 cm−1) while the calcium carbonate is totally absent. The comparative studies on the carbonation effect of the surfaces were performed on laboratory grown samples of calcium hydroxide. The samples were treated at high temperature and exposed to different ambient conditions, and the analysis suggests that the original surfaces of Roman pottery were scattered by calcium hydroxide (limewash) before the cooking
process in the furnace. The result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce the content of CO2 in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the pottery. These results give new insights on the real degree of knowledge of the Romans about the art of ceramics and more generally about chemistry and technologies.
The light-induced phase transition of TiO2 nanoparticles from anatase to rutile structure is repo... more The light-induced phase transition of TiO2 nanoparticles from anatase to rutile structure is reported depending on the surrounding environment, the transition being accomplished under oxygen-poor conditions. The transition mechanism is interpreted in the framework of oxygen adsorption and desorption phenomena with the involvement of surface oxygen vacancies and F centers. It is shown that the observed phase transition is not thermally driven because the local temperature of the nanoparticles during irradiation is about 370 K (estimated through the Stokes to anti-Stokes Raman peaks ratio). On the contrary, the phase transition is initiated by intragap irradiation (with the exception of the red light one) that acts as TiO2 surface sensitizer, promoting the activation of the surface and the nucleation of rutile crystallites starting from two activated anatase neighboring nanoparticles.
The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support ... more The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support and dissolved in distilled water solution are compared with the optical properties of the dye dissolved in ethanol and discussed on the basis of the formation of different chemical species of the dye molecule. The presence of the polymeric support affects both the absorption and emission features of the coumarin by changing the chemical equilibrium among the different species typically observed at the ground and excited states. The optical properties of synthesized PEG-supported coumarins are able to warrant biomedical applications in water-based environment and enable us to gain insight into the photophysical activity of coumarins; in particular, the steric hindrance of the polymeric support inhibits, as expected, the formation of the tautomeric form of the compound in the excited state, a further proof of the single-step neutral to tautomer reaction in coumarins.
Mixed tin–iridium oxide (Sn0.85Ir0.15O2) nanoparticles at low Ir content (15 mol%) were prepared ... more Mixed tin–iridium oxide (Sn0.85Ir0.15O2) nanoparticles at low Ir content (15 mol%) were prepared by the sol–gel preparative route, varying calcination temperatures in the range 450–550 °C. The crystal structures, the phase composition and crystallite sizes were analyzed by X-ray powder diffraction (XRD). The local order of the materials was investigated by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) analysis revealed the variation of the Ir surface state with the temperature of firing. The morphology of crystallites and the aggregates were analyzed by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM), respectively. Nitrogen physisorption by BET method was adopted to evaluate the particle surface area and the mesopore volume distribution. Electrochemical properties of the Ti-supported powders were evaluated by cyclic voltammetry (CV) and quasi steady-state voltammetry.
High-resolution photoluminescence spectra of Fe:YAG crystals were recorded in the temperature ran... more High-resolution photoluminescence spectra of Fe:YAG crystals were recorded in the temperature range 10-150 K with different excitation energies, ranging from the band gap energy (6.88 eV) down to selective excitation of Fe(3+) ions (2.40 eV). Iron levels fine structure is found in the zero phonon lines, whose characteristics hint at the presence of the doping Fe(3+) ion in the tetrahedral site with a dynamic Jahn-Teller effect inherent in the (4)T(1) excited states. The analysis of the zero phonon interactions with acoustic phonons was achieved through linear and quadratic electron-phonon coupling models, and the Huang-Rhys factor, the Debye temperature, and the electron-phonon coupling were calculated in the framework of the Debye approximation by including only the Raman two-phonon process. The interactions with lattice phonons were studied, and the results were found to be correspondent to the expected results from previous vibrational data.
Proposed herein is a method based on the Levenberg–Marquadt technique to retrieve an approximated... more Proposed herein is a method based on the Levenberg–Marquadt technique to retrieve an approximated average phonon dispersion curve from Raman spectra of nano-sized crystals. To this end we deal with a modified form of the well-known phonon confinement model in which the intrinsic linewidth Γ0 is replaced by an effective linewidth Γ. An application to experimental results obtained on TiO2
The mechanisms of porous gallium phosphide formation by anodic etching are studied. Gallium phosp... more The mechanisms of porous gallium phosphide formation by anodic etching are studied. Gallium phosphide porous samples <100> oriented were prepared in sulfuric acid solution with different concentrations of NaF. The current-voltage characteristic curve depends on the NaF concentrations and shows the typical behavior for porous semiconductors formation. Four regions can be distinguished in the I-V curve: a pore formation zone, a dielectric layer growth, a transition region in which the two processes compete for the control of the surface morphology and finally the GaP surface electropolishing. The oxide formation shifts to higher potential and the pore formation zone is widened by adding fluorides in the etching solution. Raman spectroscopy is applied to investigate the surface morphology of samples prepared in different anodizing current density conditions and in different acid solutions. As regards the dielectric growth, the direct observation of the sample surface and the analysis of the vibrational spectra indicate that in different potential regimes two chemically different oxides can be formed.
Physica Status Solidi A-applications and Materials Science, 2010
Monocrystal matrices of high-gap oxides are finding increasing applications as hosts of luminesce... more Monocrystal matrices of high-gap oxides are finding increasing applications as hosts of luminescent ions, typically rare earths (RE)s. Currently, RE-doped oxyorthosilicates, aluminum perovskites, and garnets (RE2SiO5–REAlO3–RE3Al5O12) are widely used as highly efficient and fast scintillators for γ-ray detection. On the other hand, shallow or deep intragap energy levels, due to stoichiometric deviation or impurities unintentionally added in the crystals, play a counteractive role giving rise to slower scintillation decay time, reduced light yield and afterglow. The aim of this work is to show how it is possible to tailor these unwelcome outcomes and RE-ion interactions for engineering new devices for optical memory storage. In this sense, experimental results of thermo- and radio-luminescence are presented. The role of the bandgap and the location in energy of the levels due to the RE dopants and to the defects is discussed from a theoretical point of view. The feasibility in the near future of new promising transparent displays is also discussed.
This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr... more This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr(3+) ions in an yttrium aluminium garnet (YAG) matrix. Experimental data were analysed in the framework of electron-phonon coupling in the quadratic approximation and it was found that Cr(3+) ions in the YAG matrix are strongly coupled with lattice vibrations, with a Debye temperature of about 550 K and a value of the quadratic coupling constant of 0.65. The analysis of both homogeneous and inhomogeneous contributions to the photoluminescence linewidth is performed and the results obtained are compared with previously reported data for Fe(3+):YAG and discussed with respect to the different dependences of the two transition metal ions on the crystal field.
ABSTRACT In this paper, we report the anatase-to-amorphous phase conversion of TiO2 nanoparticles... more ABSTRACT In this paper, we report the anatase-to-amorphous phase conversion of TiO2 nanoparticles by means of low intensity visible light excitation. A proper choice of power density of the incident radiation and of partial pressure of oxygen in the experimental room allows a local and precise control on the phase of TiO2 nanoparticles. The 2.54 eV light of an Ar+ laser was used to induce structural changes on the samples and to collect photoluminescence spectra, while the 1.96 eV light of a He−Ne laser was utilized for in situ Raman measurements to give immediate proof of the crystallographic structure of the samples. In opposition to other light induced processes, based on the temperature effect, the phase conversion is due to surface modifications by a proper depletion of adsorbed oxygen on the crystal surface.
Mechanically activated anatase powders were used to assemble thin film electrodes for electrophot... more Mechanically activated anatase powders were used to assemble thin film electrodes for electrophotocatalytic applications. Flat band potential of the different samples, estimated from the dependence of photopotential on the light intensity, as well as photocurrent vs potential curves were measured at samples milled for different times and compared with those of the untreated anatase. The maximum performance is achieved at
The structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO3) were inv... more The structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO3) were investigated by means of Raman spectroscopy and EXAFS measurements.The analysis of Raman spectra taken in four different polarized configurations along the principal axes at 20K and room temperature conditions permits to assign the principal vibrational modes in LuAP single crystals and to confirm the belonging to the D2h16 space group.EXAFS measurements were performed at room temperature in order to obtain local structural informations on the first and next nearest neighbors around lutetium absorptions sites. Unit cell parameters and bond lengths were determined by the analysis of the EXAFS spectroscopy at the L3 absorption edge of lutetium.The informations thus gathered on this compound can offer a useful addition in the framework of a full structural characterization of LuAlO3.
Uploads
Papers by Carlo Ricci
process in the furnace. The result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce the content of CO2 in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the pottery. These results give new insights on the real degree of knowledge of the Romans about the art of ceramics and more generally about chemistry and technologies.
process in the furnace. The result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce the content of CO2 in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the pottery. These results give new insights on the real degree of knowledge of the Romans about the art of ceramics and more generally about chemistry and technologies.