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Cadmium yellow degradation afflicts numerous paintings realized between the XIXth and XXth centuries. The degradation process and its kinetics is not completely understood. It consists of chalking, lightening, flaking, spalling, and, in its most deteriorated cases, the formation of a crust over the original yellow paint. In order to improve the comprehension of the process, mock-up samples of CdS in yellow and orange tonalities were studied by means of structural analysis and optical characterization, with the principal techniques used in the field of cultural heritage. Mock ups were artificially degraded with heat treatment and UV exposure. Relevant colorimetric variation appears in CIE Lab coordinates from reflectance spectra. XRD, SEM-EDS, and Raman spectroscopy revealed the formation of cadmium sulfate, whilst time-resolved photoluminescence and pump–probe transient absorption spectroscopy suggest the formation of a defective phase, compatible with Cd vacancies and the formation of both CdO and CdSO4 superficial clusters.

A major issue in the development of Lead halide perovskites is the assessment of the crystal structure of the samples, due to their typically limited time-stability, and the understanding of the role of external factors that can induce a crystal phase transformation (such as humidity, intense light flux, temperature, etc.). In this perspective, it is of utmost importance to have at disposal a fast and reliable experimental tool able to give an immediate indication of the polymorph of the sample with the possibility to integrate in-situ measurements for constant monitoring. In this paper we propose Raman spectroscopy as the ideal technique to solve this problem. The vibrational analysis of CsPbI3 in the α-phase and δ-phase and of the Cs4PbI6 secondary phase is reported and all the vibrational modes are assigned by comparing experimental spectra of the phases to Raman modes calculated within the DFT framework. Finally, the mechanism of laser induced phase degradation was studied using in-situ Raman measurements providing new insights on the secondary phase generated during the process.

CsPbI3 inorganic perovskite is synthesized by a solvent-free, solid-state reaction, and its structural and optical properties can be deeply investigated using a multi-technique approach. X-ray Diffraction (XRD) and Raman measurements, optical absorption, steady-time and time-resolved luminescence, as well as High-Resolution Transmission Electron Microscopy (HRTEM) imaging, were exploited to understand phase evolution as a function of synthesis time length. Nanoparticles with multiple, well-defined crystalline domains of different crystalline phases were observed, usually surrounded by a thin, amorphous/out-of-axis shell. By increasing the synthesis time length, in addition to the pure α phase, which was rapidly converted into the δ phase at room temperature, a secondary phase, Cs4PbI6, was observed, together with the 715 nm-emitting γ phase.

The development of new luminescent materials for lighting applications or stress sensors, mechano-driven lighting devices is a crucial technological topic. Materials suitable for these applications should guarantee a high chemical stability, easiness and green sintering procedure and optimal optical properties. In this framework Calcium Zinc oxysulfide (CaZnOS) represents one of the most promising materials, for its near UV excitation with a broad visible emission, a long phosphorescence and a mechano-luminescence effect that still need to be explored. In this work we report the optical properties and the kinetics of radiative recombination upon intrinsic and extrinsic excitation of pure CaZnOS, assessing the vibrational properties by means of Raman spectroscopy, and corroborated by DFT calculations. The analysis of time resolved measurements at room and low temperature (up to 10 K) give new insight on the distribution and nature of the defects that generate the luminescence upon external stress as well the long phosphorescence. Herein, we also present a model of the intrinsic defects and on the energy transfer mechanism among levels in pure CaZnOS matrix, opening new perspectives also on doped materials and for the development of piezoluminescent devices.

The molecular model is one of the most appealing to explain the peculiar optical properties of Carbon nanodots (CNDs) and was proven to be successful for the bottom up synthesis, where a few molecules were recognized. Among the others, citrazinic acid is relevant for the synthesis of citric acid-based CNDs. Here we report a combined experimental and computational approach to discuss the formation of different protonated and deprotonated species of citrazinic acid and their contribution to vibrational and magnetic spectra. By computing the free energy formation in water solution, we selected the most favoured species and we retrieved their presence in the experimental surface enhanced Raman spectra. As well, the chemical shifts are discussed in terms of tautomers and rotamers of most favoured species. The expected formation of protonated and de-protonated citrazinic acid ions under extreme pH conditions was proven by evaluating specific interactions with H2SO4 and NaOH molecules. The reported results confirm that the presence of citrazinic acid and its ionic forms should be considered in the interpretation of the spectroscopic features of CNDs.

International audience; The mechanochemical preparation of silver sulfadiazine and dantrolene, two marketed active pharmaceutical ingredients, was investigated by in situ Raman spectroscopy. For the first time, the mechanochemical transformations involving highly fluorescent compounds could be studied in situ with a high-resolution Raman system combined with a unique suitable Raman probe. Moreover, the kinetic features of the mechanochemical process were examined by a mathematical model allowing to describe the chemical changes under mechanical stress. This approach is promising both to broaden the scope of Raman in situ investigations that would otherwise be impossible and for process optimization at any scale.

Numerous experimental techniques of analysis find applications in many branches of the archaeometry. Among them, Raman spectroscopy carved out a niche in the field of diagnostic and conservation of cultural heritage. The exceptional ability to predict and discover the structural properties of materials set for Raman spectroscopy, an exclusive role among the analytic techniques, is further boosted when it is coupled with mathematical or statistical models able to deepen the studied phenomena. In this work, we present a review of recent studies where pairing Raman spectroscopy and mathematical models allowed achieving important results in the case of potteries, porcelains, ancient and modern paper, ancient jewelry, and pigment degradation. The potentialities of this approach are evidenced and analyzed in detail.

Calcium hydroxide, a crystal involved in the cycle of calcination and carbonation of calcium oxide, finds several applications from cultural heritage to the dentistry branch or to the construction industry. When excited at 1064 nm, Raman spectra of calcium hydroxide show a broad composite band peaked at about 780 cm&minus, 1, corresponding to 1170 nm. Since it is not observed with visible excitation, the origin of this band is debated, being assigned to some pre-existent luminescent impurities or some structural defect of the lime formed after the synthesis of the material. To shed light on the formation of this band, we synthetised the lime paste starting from pure calcite powders. The obtained fresh Ca(OH)2 samples did not show any band in the investigated range, irrespective of the laser excitation applied. A detailed analysis of the excitation and emission spectra in the near infrared region did not show the 1170 nm band, supporting the hypothesis of a post-synthesis origin. Thus, we carried out thermal treatments at different temperatures (90&ndash, 500 &deg, C) and under different environments (in air or under nitrogen flux) on synthesised fresh Ca(OH)2 powders. We also investigated the time evolution of the samples, monitoring the Raman spectra over 90 days after a specific treatment. The collected data support the hypothesis of a defect-related luminescence centre, whose formation depends on the temperature and environment of the treatment, which appears as a preferential site for the carbonation process of the calcium hydroxide. These results can be useful in the field of Cultural Heritage for dating purposes, and to determine the conservation state of Ca(OH)2 containing relics to prevent the possible activation of degradation processes.

International audience; Carbon Nitride and its polymorphs have recently gained large interests for their huge properties and applications in different fields, from lighting to photocatalysis. Further, several attempts were recently devoted to tune and control its optical and electrical properties. In this report we analyze phenyl modified Carbon Nitride structures obtained by simple thermal polymerization at different temperatures (250-400°C) of the starting precursor: 2,4-diamino-6-phenyl-1,3,5-triazine. A multi-technique experimental data (XRD patterns, Raman, TGA and DTG, steady-time and time resolved Luminescence, Photoluminescence Excitation spectra, Reflectivity spectra) was applied to analyze the relationship between structural and optical properties and to give more insight on the effect of synthesis procedure on the final polymer. The optical properties evidenced an interesting shift towards the visible region of the absorption spectrum of the phenyl modified g-C 3 N 4 polymer that, associated with the high optical quantum yield (about 60%) and to a broad emission in the green-red spectral region, makes the samples very suitable for lighting applications. Indeed, we report a first prototype of white LED emission by assembly of a commercial blue LED and the Phenyl modified g-C 3 N 4 powders as phosphor, verifying the structural and optical stability over about 10,000 working hours.

For many centuries, paper was considered the main support for recording cultural achievements all over the world. Archives represent the historical memory of our past, and the book conservation represents one main concern since many books and documents kept in libraries and archives are at risk because of their fragility. The use of portable, not destructive technique like NIR μ-Raman spectroscopy represents a valid instrument for monitoring the documentary heritage. In the present study, we investigated the degradation process, associated to the polymers breaking, in order to propose a successful kinetic model for determining the ageing time of cellulose. We compared the calculated results with respect to both experimental samples and literature data, covering a period of seven centuries, from XV to XXI centuries. Proposed model starts directly from Raman spectra, in particular by monitoring the band at 1100 cm− 1 ascribed to C-O-C inter-monomers bond, whose relative intensity is related to the cellulose chain length. We obtained a very good agreement with the experimental data with 8% of accuracy. Finally, with the help of Density Functional Theory (DFT) simulations, we confirmed our model by studying the structure and the grade of cellulose crystallinity in the paper. In particular, the reverse trend of the band at 900 cm− 1, related to the crystallinity grade of the cellulose, and the band at 1100 cm− 1, as a function of the dimer unit cell structure, supported the kinetic model, suggesting a shear stress like effect as the origin of the cellulose chain length decrease.

The photoreduction of 4-nitrophenol to 4-aminophenol by means of protonated and exfoliated phenyl-doped carbon nitride is reported. Although carbon nitride-based materials have been recognized as efficient photocatalysts, the photoreduction of 4-nitrophenol to 4-aminophenol is not allowed because of the high recombination rate of the photogenerated electron–hole pairs. In this paper, we show the morphology effects on the photoactivity in phenyl-doped carbon nitride. Structural (TEM, XRD, Raman) and optical characterization (absorption, photoluminescence) of the protonated and exfoliated phenyl-doped carbon nitride (hereafter pePhCN) is reported. The increased photocatalytic efficiency, with respect to the bulk material, is underlined by the calculation of the kinetic constant of the photoreduction process (2.78 × 10−1 min−1 and 3.54 × 10−3 min−1) for pePhCN and bulk PhCN, respectively. Finally, the detailed mechanism of the photoreduction process of 4-nitrophenol to 4-aminophenol by modified phenyl carbon nitride is proposed.

In this study, we proposed a preliminary kinetic model applied to the carbonation process of fresh lime with the intention to realize a diagnostic tool for aged fresco paintings. The model can be useful, in particular, in the fields of conservation and restoration of ancient lime wall paintings. The dating procedure was achieved through the analysis of 1064 nm excited Raman spectra collected on artificially aged lime samples in addition to ancient samples taken from literature and covering a period of two thousand years. The kinetic model was developed monitoring the concentration of emitting defective centers related to the intensity of 780 cm−1 calcium hydroxide band as a function of the time and depth. This preliminary model shows how Raman spectroscopy, especially NIR micro-Raman, is advantageous for diagnostics and conservation in the cultural heritage field.

Darkening of Red Vermilion (cinnabar) is a well-known phenomenon which needs, at the moment, a full comprehension of its nature. Some paintings reveal a disfiguring process of blackening degradation of Red Vermilion, albeit other relics preserve the original color during the time. The presence of halide elements like Cl− ions, in addition to the light exposure, represents the most alleged cause to explain the darkening phenomenon. However, the real effect of chlorine impurities is still not completely understood. In this study, starting from a multi-technique characterization, we propose a kinetic model of mutual composition of alpha/beta cinnabar derived by the experimental darkening of pure alpha synthetic cinnabar intentionally doped with Cl− ions and treated under prolonged UV light exposure. The model was further applied to ancient samples by analyzing the Raman spectra of antique cinnabar pigments belonging to manuscripts of XIII-XVII centuries.

Graphitic carbon nitride (g-C3N4) is considered as one of the most promising photocatalysts for environmental improvement and energy storage. It presents a graphene – like 2D structure, composed of heptazine units connected by amino groups. Here we report multi-technique experimental data (XRD patterns, Raman, steady-time and time resolved Luminescence, Photoluminescence Excitation spectra, Reflectivity spectra) to analyze the relationship between structural and optical properties. We found that the low temperature phase of carbon nitride, namely Melem, presents the main optical features shifted towards higher energies with respect to the higher temperature phase, i.e. Liebig's melon structure or Polymeric Carbon Nitride (PCN). Time resolved luminescence in the ns-domain was therefore exploited to further analyze the kinetics of the excitons generated during optical excitation. Two decay trends were observed in both the structures, with decay time constants depending on sample structure and cell parameters: the faster component, with sub-nanosecond decay time, is related to the recombination from the σ* band whilst the slower decay time is assigned to recombinations within the single triamino-tri-s-triazine unit. The correlation between structural parameters and optical properties is discussed and a model on the optical levels is proposed.

A new promising inert matrix as host of luminescent ions is proposed. Al2SiO5 samples, doped with rare earths (Ce, Tb single doped and co-doped) are proposed as good prospect for the development of new UV–vis converter with reduced content of rare earths elements. Structural characterization by Raman, XRD spectroscopy and TEM imaging reveals the sillimanite phase and nano sized dimension of the investigated powders. Optical characterization by steady time and time resolved emission spectroscopy for the single doped and co-doped samples allows to identify an efficient energy transfer from Ce to Tb ions under near UV excitation wavelength. The intense green emission observed in the Ce:Tb co-doped Al2SiO5 system suggests its potential application as efficient blue pumped green emitter phosphor to be exploited for white LED: to this purpose we tested the compound in combination with a red emitting doping ion recording for Ce:Tb:Cr:ASO system a correlated color temperature of 6720 K.

We applied micro-scale Spatially Offset Raman Spectroscopy (micro-SORS) to perform the analysis of the layer composition in a fresco of the San Giuseppe church in Cagliari (XVIII century – under restoration). Standard Raman analysis of the surface evidenced the presence of expected pigments in the final plaster layer, such as hematite and calcium sulphate, beside the contribution of calcite. The second one is observed in its anhydrous form on the substrate layers (main Raman peak at 1024 cm−1) and in its hydrate form (1006 cm−1) from the surface. With micro-SORS analysis we evaluated the stratigraphy of the different layers of the plaster by monitoring the intensity ratio of the calcite and the anhydrous calcium sulphate. Four different layers with separation boundaries at about 80 μm, 600 μm and 2400 μm of defocusing distance were evidenced, corresponding to the painting layer “velo”(down to 80 μm), the plaster “rasatura” (down to 600 μm), the “arriccio” layer (down to 2400 μm) and the “rinzaffo” layer (below 2400 μm). The cross-sectional analysis by SEM imaging of a fragment from the fresco confirmed the micro-SORS findings, promoting the technique as a new non-invasive stratigraphy tool for cultural heritage.

Portable Near Infrared Micro-Raman (NIR μ-Raman) spectroscopy was used, as a preliminary and non-destructive technique, in order to investigate the mineralogical composition of a group of pottery sherds from Khirbat Iskandar, Jordan. Preliminary results show that the ceramic body is composed mainly of quartz, calcite, and minor amounts of feldspars and hematite. In addition, the presence of Olivine and anatase, important markers to identify the provenance of raw materials, was detected. Furthermore, the occurrence of Portlandite was related to both rehydration of calcite and burial alteration processes. Finally, a study of Raman spectrum of Amorphous Carbon, identified as temper in the clay, was performed to estimate the manufacturing parameters (maximum temperature and permanence time).

The mechanical stress in nanosized silicon architectures is studied in shallow trench isolation systems with different liners and spin on dielectrics processed silica filler by means of Raman spectroscopy. The nanopatterning of silicon wafers causes a tensile stress of the system whereas the presence of the filler induces a compressive stress which depends on the interaction between silica filler and liner: by changing the liner from silicon dioxide to silicon nitride one can induce a larger compressive stress. The analysis of the ultraviolet excited emission properties in the visible range (nanosecond lasting bands at 2.5, 3.0 and 3.3 eV) allowed us to individuate and locate silica related defects and to correlate their presence to the induced compressive stress.

The structural evolution of γ-Fe2O3 (maghemite) in bare nanoparticles and in core/shell γ-Fe2O3/SiO2 systems was studied as a function of laser irradiation and heat treatment by the combined use of Raman spectroscopy, transmission electron microscopy, X-ray diffraction. The study was addressed to deepen understanding the driving mechanisms at the basis of the maghemite to hematite (α-Fe2O3) phase transition and to understand the possible correlation with surface/defects states. In the bare system, phase transformation was obtained with very low beam density powers (less than 2 mW at 632.8 nm focalized with a conventional 10× microscope objective) and the threshold for transition further decreases in vacuum conditions, suggesting that the phase transformation can be achieved even without thermal assistance. On the contrary, phase transformation cannot be obtained by light irradiation in a γ-Fe2O3/SiO2 core/shell system, but it can be induced by heat treatment at very high temperature (1100 °C). Fe2O3 nanop...

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 CO2in 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 structural and optical properties of sol–gel synthesized TiO 2 nanoparticles doped and co-doped with N and rare earth ions (Y 3+ and Pr 3+ ) are presented. Crystal structures, phase composition, and crystallite sizes are analyzed by powder X-ray diffraction and Raman spectroscopy. The analysis of intragap excited photoluminescence indicates the formation of radiative recombinations related to different defect centers in the TiO 2 structure, generated by the presence of doping elements. In particular we assign the formation of bulk and surface defects to the presence of nitrogen in the TiO 2 matrix, whereas we observe different effects on the defective TiO 2 structure related to the two rare earths: the presence of Y 3+ ion acts as a stabilizer of the TiO 2 surface whereas the presence of Pr 3+ generates surface recombination centers.

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 structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO 3 ) 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 20 K and room temperature conditions permits to assign the principal vibrational modes in LuAP single crystals and to confirm the belonging to the D 2 h 16 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 L 3 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 LuAlO 3 .

We present the first report about growth and optical properties of pure Ytterbium Alluminium perovskites single crystals (YbAlO3). The sample crystal structure was studied and assigned by means of Raman spectroscopy while the photoluminescence measurements from Yb3+ charge-transfer state show a broad ultraviolet emission bands with nanosecond lifetimes at room temperature. Yb emissions are also studied as a function of temperature revealing an abrupt quenching in the 180–240 K range. The fast time decay and the high material density suggest Ytterbium Alluminium perovskites crystal as a good candidate for the development of fast scintillators for high energy physics applications.

Nanocrystalline WO3 samples are synthesized by different procedures. The first series of samples are obtained by sol-gel reaction, starting from WCI6, followed by thermal treatments in the range 300-750 degrees C. To improve the oxide microstructure, a second series of samples is obtained by submitting the xerogels, obtained from the sol-gel reaction, to prolonged (170 h) hydrothermal (HT) growth steps in the presence of a surfactant, either non-ionic (Lutensol ON70) or ionic (cetylpyridinium chloride), and to a final firing. The HT treatment, in the presence of cetylpyridinium chloride is also combined with Ag promotion (1% Ag). The phase composition of all samples is characterized jointly by XRD Rietveld refinement and Raman spectroscopy. The observed different temperature domains of the nanocrystalline WO3 polymorphs with respect to bulk systems are attributed to the occurrence of surface relaxation phenomena. TEM and SEM images show that the samples submitted to the surfactant HT treatment present a generally improved microstructure while the presence of Ag induces crystallite growth and sintering between the particles. The NO2 sensing measurements show for all samples that the film response decreases with the operating temperatures and is promoted by the presence of humidity. The samples obtained by the surfactant HT treatment show a much better sensor performance with respect to the other samples, the more so in the case of the cationic molecules. The role played by the HT treatment in promoting the features of the WO3 samples is discussed also on grounds of Raman analyses in the water-OH stretching region.

Raman spectra in Sn 1− x Ir x O 2 ( x ⩽ 0.15) nanocrystals were investigated to estimate and separate the contributions of phonon confinement and composition effects. To this end, the Raman frequency of the A 1 g bulk-mode of pure SnO 2 and Ir-mixed nanocrystals has been studied in details as a function of the size and the Iridium concentration. As an initial working hypothesis it was assumed a linear dependence of the Raman shift as a function of the Iridium molar concentration, while a quadratic expansion of the dispersion curve has been utilised in the phonon confinement effect. Comparison of predicted and experimental results is reported.

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.

Raman spectra of nanocrystals titanium dioxide are discussed and the correlation between the band shape of the allowed A1g Raman mode and the crystals dimensions is discussed. Data on Raman spectra are reconsidered in the frame- work of a modified "hard confinement" model (MHC). The proposed model is based on the idea of using an effective linewidth parameter, which is a function of the effective dimension of the nanostructure, in spite of the intrinsic Raman band linewidth. The comparison with standard hard confinement model reveals better agreement with the experimental results for the MHC model up to 6 nm. Moreover, the analysis permits to improve the knowledge of the phonon dispersion curve as well as the intrinsic Raman bulk parameters. An analytical form of the size-dependent peak-position in nanocrystals, useful for an approximated size estimation, has been explicated. The general structure of the model permits to extended the MHC to other nano-sized materials.

Lutetium yttrium orthoaluminate perovskite [Lu0.7Y0.3AlO3 (LuYAP)] crystals show great potential as fast response and high-efficiency scintillators as an alternative to LuAlO3 (LuAP) crystals. This paper aims to offer a complete analysis of the vibrational modes of the LuYAP crystal by means of polarized Raman spectroscopy in the temperature range of 20–290 K and confronting the experimental results with numerical methods in order to characterize the crystal structure. Furthermore, an interpretation of the data in terms of vibrating molecular structures is suggested and the results are successfully confronted with the vibrational modes of similar perovskite crystals. Copyright © 2009 John Wiley & Sons, Ltd.

The Raman scattering from Lu1.8Y0.2SiO5 single crystals was investigated for quasi-hydrostatic pressures ranging from atmospheric to about 15 GPa at room temperature. The material, originally belonging to the monoclinic C2/c structure, transforms gradually to a higher-density phase upon the application of pressure. Unit cell volume, peak position, and the Gruneisen parameter have been calculated and analyzed, revealing three different pressure regimes. The first low-pressure regime relates mainly to the change of unit cell volume. In the second pressure regime, the gradual phase transformation starts at about 3 GPa and is completed at a pressure of 10 GPa. The third pressure regime part reveals a sensibly lower pressure dependence. A detailed analysis of the data allowed us to propose a scheme for a pressure-induced gradual phase transition, resulting in the coexistence of phases over a wide pressure range. Moreover, the material reverts to the ambient-condition phase upon release of pressure, showing an almost total reversibility. By comparison with the vibrational spectra of the pure Y2SiO5 compound and from the analysis of the crystal structures, the pressure-induced high-density phase is assigned to the P21/c monoclinic structure, typical of oxyorthosilicates. Copyright © 2008 John Wiley & Sons, Ltd.

In this work we investigate the structural properties of Ce:Lu2(1−x)Y2xSiO5 (LYSO) crystals as a function of cerium incorporation by means of low-temperature high-resolution Raman measurements. Czochralski grown single-crystal LYSO samples were obtained with a ratio of yttrium to lutetium ions 10:90 (Ce:Lu1.8Y0.2SiO5) and a variation in the cerium concentration in the 0–750 ppm range. A red shift of the Raman bands, related to a decrease of the unit cell, is observed as function of the cerium concentration in the crystal. By analyzing the low wave number vibrational modes and the polarized Raman measurements, the substitutional role of cerium ions in the rare-earth sites occupied by yttrium ions is infrared. In addition, since the rare earth can occupy two independent different crystallographic sites, the analysis of the Raman spectra allows to distinguish the preferred site by cerium ions in the doping process.

Nanocrystalline CaF 2 were obtained by ball-milled synthetic fluorite powders. Raman spectra of nanocrystals with average sizes of 10–25 nm are reported and the correlation between the band shape of the only allowed Raman mode at 322 cm −1 and the crystals dimensions is discussed. While in such systems local temperature and pressure effects play a minor role, variations in the shape of the Raman band can be correctly reproduced by a model based on the phonon confinement that effectively takes into account the anisotropy of the phonon dispersion curve.

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 pigments 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.

The paper presents the results on the evolution of electronic features and electrochemical activity of boron doped diamond samples during oxidative ageing tests. For 1 cm 2 of electrode surface, the resistance increases from 7 Ω to about 200 Ω during the first hour of work, than it decreases down to 2 Ω in 350 h. In this condition, high values of heterogeneous electron-transfer rate constants for ferro/ferricyanide are measured in the order of 10 − 4 cm/s, indicating a semi-metallic behaviour of the samples. Results from Raman analyses are also presented and a possible explanation of the observed behaviour of the samples is proposed, in terms of both the intrinsic movement of the H within the structure of the film and the variation of free acceptor levels associated to the B atoms in the lattice.

Owing to its unique properties such as chemical stability, large potential windows of water stability (up to 3 V) and mechanical resistance, boron-doped diamond (BDD) thin films have been widely used as electrodes for electro-analysis and electrolysis. In this work we have studied surface structural modifications in BDD thin films grown by hot filament chemical vapor deposition (HFCVD) due to usage as anodic working electrode in H3PO4 aqueous solution (pH=1, 2) up to 1000 h. With the powerful tool of Micro-Raman spectroscopy we show nonuniform structural variations of the diamond lattice. Modifications in the electrochemical properties has been observed while BDD electrodes were used as anodes. Moreover, by modelling the Fano interaction between discrete phonon states and the degenerate continuum of states, we point out an increase of the acceptor levels as a function of the electrode working hours. These experimental evidences indicate an anomalous behaviour of hydrogen loaded in the films during the growth process. A model based on the hydrogen–boron interaction could explain the observed modifications in Fano coupling.

The surface vibrational properties of sol–gel synthesized porous silica are investigated as a function of sample porosity. By considering the Raman contribution of the physisorbed water, the analysis of the fundamental O–H stretching range (3000–3800 cm−1) displays the vibrational modes related to Si–OH species on the surface of the porous matrix. The sample porosity affects the H-bonding interaction between OH-related groups and influences the hydrophilic character of the surface: a curvature effect can be hypothesized.

Surface in porous media has a key role for both theoretical and technological aspects. A comparative analysis of the surface vibrational properties of sol−gel synthesized porous silica monoliths with different porosity is presented. Raman spectroscopy investigation of the fundamental O−H stretching range (3000−3800 cm-1) reveals a dependence of the surface reactivity on pore dimensions. The pore surface curvature plays an important role affecting the hydrogen-bonding interaction between surface hydroxyls and modifying the distribution of the OH species at the surface; the relative contribution of interacting hydroxyls and adsorbed water with respect to isolated species is larger in smaller pores. Water and silanol vibrations were singled out as a function of porosity.

Porous layers fabricated by electrochemical anodization of (111)A-oriented n-GaP:Te substrates were studied by Raman scattering spectroscopy in the temperature interval from 10 to 300 K. Along with the transverse-optical (TO) and longitudinal-optical (LO) modes, the RS spectra of porous layers show Frohlich-type vibrations located in the frequency gap between the bulk optical phonons. A longitudinal-transverse splitting of these surface-related vibrations was evidenced at low temperatures. Apart from that, the porous layers prepared on highly doped substrates were found to show LO-phonon-plasmon coupled (LOPC) modes in the whole temperature interval studied. Observation of LOPC modes at low temperatures is explained taking into account that the GaP skeleton consists of both depleted surface layers surrounding the pores and conductive regions. The free electrons in these regions, originating from the impurities actually located in the depletion layers, are shown to be subject to spatial confinement increasing with decreasing temperature.

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 Γ 0 is replaced by an effective linewidth Γ . An application to experimental results obtained on TiO 2 nano-crystals is presented as a test of the method.

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.

The structural and vibrational properties of Lu{sub 1.8}Y{sub 0.2}SiO{sub 5} (LYSO) single crystals were investigated by means of Raman spectroscopy and x-ray diffraction measurements. Unit cell parameters and bond lengths were determined by Rietveld refinement of the collected x-ray diffraction powder spectra. By comparison with the vibrational spectra of the parent compounds Lu{sub 2}SiO{sub 5} and Y{sub 2}SiO{sub 5} and by using polarized Raman measurements, we propose the assignment of the principal vibrational modes of LYSO crystals. The strict connection of Raman spectra of the LYSO solid solution and of the pure lutetium and yttrium crystals, as well as the analysis of the polarized measurements, confirms that LYSO structure adopts the C2/c space group symmetry. The structural analogies of LYSO with the pure compound Lu{sub 2}SiO{sub 5} are further shown by means of high pressure Raman spectroscopy, and the possibility of considering the LYSO crystal analogous to the LSO structure with a tensile stress between 0.25 and 0.80 GPa is discussed.

The phenomenon of luminescence enhancement was studied in melamine-Y2O3:Tb hybrids. Terbium doped Y2O3 mesoporous nanowires were synthesized by hydrothermal method. X-ray diffraction patterns and Raman scattering spectra testified the realization of a cubic crystal phase. Organic-inorganic melamine-Y2O3:Tb3+ hybrid system was successfully obtained by vapour deposition method. Vibration Raman active modes of the organic counterpart were investigated in order to verify the achievement of hybrid system. Photoluminescence excitation and photoluminescence spectra, preformed in the region between 250 and 350 nm, suggest a strong interaction among melamine and Terbium ions. In particular, a remarkable improvement of 5D4→ FJ Rare Earth emission (at about 542 nm) of about 102 fold was observed and attributed to an efficient organic-Tb energy transfer. The energy transfer mechanism was studied by the use of time resolved photoluminescence measurements. The melamine lifetime undergoes to a significant decrease when ...

TiO(2) nanoparticles are obtained by combining a sol-gel preparative route with hydrothermal aging steps, performed in mild conditions, of varying time lengths. Both aged and un-aged samples are thermally treated at 300 and 600 degrees C, for the same length of time. The crystal structures, the phase composition, and crystallite sizes are analyzed by powder X-ray diffraction. Raman spectra of anatase nanocrystals with average sizes of 7-10 nm are reported and the correlation between the Raman band shape of the main feature at 144 cm(-1) and the crystallite size is discussed. Nitrogen physisorption by Brunauer-Emmett-Teller (BET) method is adopted to evaluate the particles surface area and mesopore size and size distribution. The role played by the hydrothermal step in affecting the physicochemical properties of the powders is discussed also with respect to the H(2)O/TiO(2) interactions as apparent from Raman spectroscopy investigations of the O-H stretching range (3000-3800 cm(-1)).

The mechanisms of porous gallium phosphide formation by anodic etching are studied. Gallium phosphide porous samples 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.

The optical and structural properties of sol–gel prepared polycrystalline films of Cerium doped Lutetium and Yttrium oxyorthosilicates (Ce:LYSO) are investigated by means of optical spectroscopy, XRD diffraction and Raman spectroscopy. The sol–gel samples are compared to commercially available Ce-doped LYSO single crystals, and a detailed study of the emission properties from the different cerium sites is performed. The main result is that the polycrystalline films do show very good radioluminescence properties for possible applications as X-ray scintillating panels. The structural characterization indicates that the sol–gel polycrystals have similar phase composition to commercial monocrystals; concerning the excitation and emission properties, the same radiative recombination channels are observed in the polycrystals and commercial monocrystals with a slightly faster decay time in the first case. In addition, low temperature measurements (8 K) indicate the presence of a non-radiative cross-relaxation mechanism among cerium ions in the sol–gel grown samples in the two possible crystallographic sites. The results indicate the possibility to develop sol–gel synthesized polycrystalline thin films as scintillating materials in the X-ray energy range.

The vibrational properties of yttrium aluminum garnet (YAG), yttrium scandium gallium garnet (YSGG), and mixed (YAG)x–(YSGG)1−x structures (0

The electrochemical etching process of porous gallium phosphide was studied by means of the characteristic current–potential (I–V) curves. Measurements were performed in H2SO4 0.5‐M aqueous solution both in the dark and by illuminating the samples with the 351‐nm line of an argon laser. Raman spectroscopy was applied to investigate the surface morphology of the samples prepared under different anodizing conditions within the potentiostatic regime. Based on a few reasonable assumptions, a simple model of pore growth is proposed. The enhancing effect in current intensity due to the branching of pores and the opposite effect due to a concomitant decrease in the effective cross area available for carrier transport are accounted for to explain the main features of the recorded I–V curves.