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In this work, we unveil the fluorescence features of citric acid and urea-based Carbon Dots (CDs) through a photo-physical characterization of nanoparticles synthesized, under solvent-free and open-air conditions, within silica-ordered mesoporous silica, as a potential host for solid-state emitting hybrids. Compared to CDs synthesized without silica matrices and dispersed in water, silica-CD hybrids display a broader emission in the green range whose contribution can be increased by UV and blue laser irradiation. The analysis of hybrids synthesized within different silica (MCM-48 and SBA-15) calls for an active role of the matrix in directing the synthesis toward the formation of CDs with a larger content of graphitic N and imidic groups at the expense of N-pyridinic molecules. As a result, CDs tuned in size and with a larger green emission are obtained in the hybrids and are retained once extracted from the silica matrix and dispersed in water. The kinetics of the photo-physics under UV and blue irradiation of hybrid samples show a photo-assisted formation process leading to a further increase of the relative contribution of the green emission, not observed in the water-dispersed reference samples, suggesting that the porous matrix is involved also in the photo-activated process. Finally, we carried out DFT and TD-DFT calculations on the interaction of silica with selected models of CD emitting centers, like surface functional groups (OH and COOH), dopants (graphitic N), and citric acid-based molecules. The combined experimental and theoretical results clearly indicate the presence of molecular species and surface centers both emitting in the blue and green spectral range, whose relative contribution is tuned by the interaction with the surrounding media.

Undoped and Zr-doped BaTiO powders have been prepared by self-propagating combustion synthesis from suitable precursors. The obtained powders have been subjected to thermal annealing in air at temperatures between 400 and 1200 °C. Experimental findings indicate that annealing affects compositional, structural and optical properties. XRD analysis reveals the presence of a metastable hexagonal phase in powders obtained by SHS. Its relative amount drastically decreases during high-temperature annealing. As-synthesized powders have broad photoluminescence due to the degree of structural order in the powders. This can be also seen from the absorbance spectra, which exhibit a band at 650 nm. F color centers form as a consequence of electron trapping in oxygen vacancies.

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.

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 study of new phosphors requires in-depth knowledge of the mechanisms and radiative emission paths and, with this aim, the study here reported focuses on the emission properties of CaZnOS crystals single doped with Terbium and co-doped with Terbium and Europium. By studying the optical properties and, in particular, the kinetics of recombination with time-resolved luminescence, the de-excitation mechanisms and the charge transfer processes have been established. A fundamental role is played by the defective centers and their efficient energy transfer process to the excited levels of Terbium, the mechanism being also active among co-doping rare earths (from Tb3+ to Eu3+), allowing further tuning of the emission properties. Beside photoluminescence, the study shows that in case of mechanical stimulus as well, the mechano-luminescence follows the same path, where the defective states of the matrix efficiently excite the levels of dopants, producing a green emission at 545 nm from Tb3+ and a red emission above 600 nm from Eu3+. Therefore, studying the relative ratio of dopants, it is shown how precisely tune across the visible part of the spectrum the mechano-luminescence emission.

Raman spectroscopy has been utilized to study ancient documents conserved at the University Library of Cagliari (Italy) with the aim to give an exhaustive scenario about the employment of inks, pigments and supporting materials (papers and parchments) related to specific historical periods (XIV–XV centuries). The samples studied are selected between the most prestigious texts present in the collection: two accounting books of sixteenth and fifteenth centuries, a mathematical text of the sixteenth century, a navigation text of the same period, a copy of the most important Sardinian medieval constitutional text “Carta De Logu”, a medieval copy of the famous Italian poem: “La Divina Commedia”. Finally we characterized a declared false of the nineteenth century reproducing a famous document of the XIII century. The present study gives fundamental knowledge on the history of different inks used in the manuscripts and also on the conservation as well degradation of supporting materials. In addition we focused our characterization on different techniques and materials applied in previous restorations. Finally, we certified with modern techniques the presence of deliberate falsification processes of some specimens.

Despite their great potentiality, ISFET-like devices generally suffer from an intrinsic limitation in sensitivity, the so-called Nernst limit. Moreover, the high costs, the restricted range of employable materials associated to the silicon technology, and the need for a reference electrode, have reduced the applicability of such devices in the bio-sensing field. In this work, we show how a reference-less pH sensor based on an organic semiconductor device, called Organic Charge-Modulated Field-Effect Transistor (OCMFET), besides being low cost, flexible, and transparent, shows a super-nernstian sensitivity with no need of any chemical modification of the sensing area. Moreover, thanks to its peculiar transduction principle and structure, the device sensitivity can be easily tuned by acting on geometry-related parameters of the device itself, introducing an interesting alternative approach for the realization of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications.

The UV excited emission properties of mesoporous silica in the blue and UV range are modified by the adsorption and desorption of oxygen molecules at the two defect sites. To interpret the experimental purging cycles we model the oxygen-silica interaction at thermodynamic level, succeeding in explaining the interaction mechanism and the trend of UV centre to undergo photo-bleaching when excited under vacuum conditions. The analysis called for the presence of two different set of defects for both the centres, pinpointed as defects liable to interact with O 2 and non-interacting isolated defects. To support the thermodynamic analysis, we simulated the O 2 adsorption and desorption processes within the first principles DFT cluster framework. The calculated atomic configurations and the potential energy curves along selected probable reaction paths allow suggesting the kinetics of molecular oxygen interaction on examined surface silica defects and pointing at an oxygen vacancy E’-like defect as the possible result of the UV centre photo-bleaching.

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.

The fluorescence properties of colloidal sealed Rhodamine 6G doped mesostructured silica nanoparticles prepared by a one-pot templated base-catalyzed sol–gel self-assembly method are reported. The hybrid organic–inorganic nanoparticles is tested against water and alcohols dye leaching showing larger resilience to leaching in water, high quantum yield despite the large dye concentration and huge relative brightness up to 1.5 × 10 5 emitting molecules per nanoparticle. This super fluorescence is 3 times larger of comparable systems and 100 times larger than the fluorescence of CdSe/ZnS quantum dots. The surfactant used for the formation of the mesostructure plays a key role both as dye splitting element and as sealing agent against leaching effect. The resilience to dye leaching in water is further justified by the formation of core–shell architectures made up of mesoporous core and homogeneous low-porous silica shell of 5–12 nm in thickness due to long aging condensation reaction of surface silanols in water. In addition, the comparison with a reference no-doped silica sample points out a possible alternative synthetic strategy to tune the structural, morphological and textural properties of silica-based nanosystems: properly engineering can exploit the effect of dye molecules addition on nanoparticles mean size, polydispersity and mean thickness of matrix silica walls.

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.

The luminescence properties of Tb and Ce in Rare Earth Doped crystalline oxides largely depend on their relative concentrations: by increasing the dopant concentration, the luminescence profile changes from blue to green because of the energy transfer among centers. The kinetic properties of the luminescence of optically excited Terbium–Cerium co-doped Y2SiO5 sol–gel synthesized crystal powders have been investigated as a function of the Tb dopant concentration (Ce content fixed at 1% atomic). The interaction among different Tb emitting centers and their relation with Ce centers was explained within the Inokuti-Hirayama model for a dipole–dipole energy transfer mechanism in the low-middle Tb concentration range whilst the Forster–Dexter model was applied in the middle-high Tb concentration range. The kinetic model allows elucidating the role of sensitizer and activator ion as a function of Tb concentration, successfully estimating the energy transfer mechanism efficiency and calculating the critical Tb concentration.

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.

This work focuses on a particular behavior of dense yttria samples fabricated by spark plasma sintering, which display a reddish coloration when subjected to X-ray irradiation. The reddish coloration appears exclusively in sintered material. Optical measurements, X-ray photoelectron spectroscopy and chemical methods have been used to investigate the properties of consolidated yttria. The results obtained suggest that the sintered material exhibits a relatively high concentration of oxygen vacancies. Thermoluminescence measurements indicate that they act as electronic trapping sites. A generalized-order kinetic analysis suggests that at least five different shallow traps can be identified.

The emission properties of mesoporous silica with different pore diameters (3.2 and 18.2 nm) are investigated under different environmental conditions, namely after long air exposure (aging process) and oxygen purging. Beside the reduced optical transparency in the visible range, the emission properties of aged samples with larger pores show a larger contribution of the UV band peaked at about 320 nm with respect to the blue one peaked at about 400 nm and a larger sensitivity of the overall emission spectrum to the oxygen purging. The aging of the samples and the sensitivity to oxygen purging are discussed in terms of the distribution of silanol groups and the curvature of the silica surface in the two sets of samples.

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.

Poly(3,4-ethylenedioxythiophene) (PEDOT) polymerization has been carried out both in a template-free environment and inside the nanopores of SBA-15 mesoporous silica. Comparing the two methods and the secondary doping of commercial PEDOT:PSS, we were able to study the structural effect of the templated polymerization via a multi-technique approach. We found that the confined polymerization favours a more linear configuration of the polymer chains, in a similar way to the well-known secondary doping with organic solvents. Moreover, comparison of computational and experimental results suggests that the PEDOT mean chain length is greater when the polymerization occurs in the nanoporous template, promoting the formation of a polymer with larger molecular weight and crystallinity.

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.

In this work polysilazane based silica thin films grown on multilayer structures of different ultra-thin barriers (UTBs) on silicon substrates were studied. The silica thin films were obtained by polysilazane spin coating deposition (also called SOD, spin-on dielectrics) upon different UTB liners (silicon nitride or silicon dioxide). By curing the SOD with thermal treatments the polysilazane is converted into silica thin films. The degree of conversion to SiO 2 was analyzed and the oxide local structure was studied in terms of Si O Si bridges by FTIR spectroscopy. Steady state and time resolved luminescence were applied to further characterize the oxide structure, the substrate–silica interfaces and the presence of defects. The analysis revealed the presence of dioxasilirane, Si(O 2 ), and silylene, Si:, defect centers in the samples grown on silicon nitride UTB, while these defects are not observed in samples grown on silicon oxide UTB.

In this work the synthesis of hybrid electrodes obtained by electrochemical functionalization of nanotubular TiO 2 arrays with diazonium salt and subsequent sensitization with Coumarin is proposed. Nanotubes are grown by electrochemical anodization of Ti foils. Anodization is performed at 35 V in ethylene glycol solution and in the presence of fluoride ions. The results obtained in the present study indicate that the functionalization with diazonium allows itself an enhancement of the current yield of the water electrosplitting process. Photocurrents further increased after the sensitization of the samples with Coumarin dye, so indicating good chances for possible applications of the electrodes in DSSC.

In this Letter the optical properties of a new hybrid electrode based on Coumarin 153 adsorbed on nanotubular TiO 2 arrays are presented. The absorbance measurements show an enlargement in the visible spectral range and the photocurrent response is sensibly increased with respect to pure TiO 2 nanostructure; moreover, the analysis of the luminescence spectra suggests the formation of Coumarin aggregates on TiO 2 surface. The mechanism of the fast injection of photoexcited electrons from the Coumarin excited levels to the TiO 2 conduction band was studied and, based on absorption, emission and photocurrent data, a strong coupling between the two components is proposed.

The local environment around Yb3+ ions in silica-based optic fibre preforms has been studied in specimens with different composition and submitted to different annealing processes. The formation upon annealing of nano-sized particles of YbPO4 has been evidenced by X-ray Absorption Spectroscopy whereas optical luminescence present Stark-split states in the anti-Stokes lines, typical of a structurally ordered phase. This evidences the preferential location of Yb in highly coordinated phosphate environment, with remarkable effects of such ordered phase on the optical response of the system. This study confirms and extends analogous observations done in previous literature on Erbium in similar glasses.

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.

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.

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.

In this work we report for the first time the fluorescence properties of Ce 3+ single-doped and Ce 3+ /Eu 2+ co-doped BaGa 2 S 4 crystals, studied by means of time resolved measurements. The single-doped samples fluorescence was characterized by the Ce 3+ radiative transitions from the 2 D level to the 2 F 5/2 and 2 F 7/2 levels with a lifetime of 18 ns, and by a radiative transition from the E g level to the ground state of Ce 3+ ions with a lifetime of 11 ns. The co-doped samples fluorescence was characterized by Eu 2+ radiative transition from 4f 6 d state to the ground state with a lifetime of 290 ns. Ce 3+ emissions in co-doped samples are strongly quenched and a lifetime of 6 ns is observed. The reported data are discussed in the framework of energy transfer process between Ce and Eu. The rate of the energy transfer was estimated in 7.5 × 10 7 s −1 with efficiency of 66%.

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.

By exciting with synchrotron radiation in the 4–10 eV range the emission properties of sol–gel synthesized porous silica at room temperature and at 8 K are investigated. The modifications of the ultraviolet emission in the range 3.7–4.2 eV excited at different energies (5.64, 6.20, 6.53, and 6.89 eV) support the hypothesis of the contribution of two emitting centers. In particular the two emissions are spectrally resolved when exciting at 5.64 eV and a blue shift of the emission peak is reported as the excitation energy increases. The analysis of the decay times indicates that the two centers are temporally resolved with the 5.64 eV excitation both at room temperature and at 8 K and allows to estimate lifetimes of about 3 and 18 ns. When exciting at 6.53 eV, the larger relative contribution of the 4.0 eV band does not allow to efficiently resolve the two decay times and the estimated life time of the 3.8 eV band is shortened.

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.

Silver thiogallate (AgGaS 2 ) is a ternary semiconductor which crystallizes in the chalcopyrite structure. Silver thiogallate has been widely used in different applications for its interesting physical properties: wide transparency range (from 0.5 to 12 μm), high non-linear optical coefficient combined with good mechanical properties. The direct band gap in this compound is of about 2.7 eV and emissions due to free and bound excitons had been observed. Photoluminescence spectrum is also characterized by a wide emission band centred at 496 nm (2.50 eV) due to donor–acceptor pairs recombination (DAP). We performed photoluminescence (PL) measurements exciting with the third harmonic (3.5 eV) of a Nd:YAG laser from room temperature down to 10 K at different excitation power. In this work, we report the dependence of the photoluminescence features of AgGaS 2 on the excitation power at various temperatures: ionization energy of defects are estimated on the basis DAP theoretical model and of thermal quenching of the photoluminescence; evidences of non-radiative processes competitive to DAP is also presented.

A detailed study of the polarized Raman scattering of wurtzite GaN films is presented, focusing on the nature of the band centered at 740 cm −1 observed in the X ( Z , Z ) X configuration. The origin of this band is ascribed to the mixed contribution of the A 1 and E 1 longitudinal phonon modes coupled with the free carrier excitation. The spectral profile of the 740 cm −1 Raman band has been successfully reconstructed through a linear combination of the A 1 –E 1 longitudinal phonon plasmon-coupled modes, leading to a free carrier concentration in good agreement with Hall effect measurements.

In the last decades solid-state tunable lasers were prepared by embedding dye molecules into sol–gel matrix. The main advantage with respect to the liquid dye solution is the decrease of health and environmental hazards. However the desired dye photostability, which is mainly related to the photochemical degradation of organic molecules in their gain range, has not yet achieved. In this work we present a photostability study of porous silica – rhodamine 6G hybrids (PS-R6G) prepared via sol–gel method. Two kinds of samples were prepared: class I and II, where the dye molecules are weakly and covalently bonded to the glass matrix, respectively. Measurements were carried out by exciting PS-R6G samples with the 3rd harmonic of a Nd:YAG laser (355 nm) at different power densities. We observed the decay of the fluorescence signal as the cumulative excitation energy increases in both the sets of samples. The photobleaching rate depends both on the power density and the kind of the samples. The photoluminescence properties and the photobleaching feature reported indicate the class II samples as good candidate for solid-state dye laser.

The photoluminescence properties of porous silica at low temperature (8 K) are investigated as a function of the porosity of the samples. At 8 K the contribution of the emission at about 2.8 eV with respect to the luminescence at 3.7 eV increases allowing its spectral resolution. The shift of the peak position of the emission at about 2.8 eV at different excitation energies and the non single exponential law of its decay time suggests the presence of two different surface centers.

The photoluminescence properties of sol–gel prepared porous silica in visible and ultraviolet range were studied exciting in the 4–8 eV range by means of synchrotron radiation. Two main emissions at 2.8 and 3.7 eV were detected and studied as a function of the temperature from 8 up to 300 K. The two emission bands displayed different excitation channels: at 5.6 and 6.2 eV for the 3.7 eV band and at 4.8, 5.2 and 6.0 eV for the 2.8 eV band. By increasing the temperature the amplitude of the 2.8 eV emission decreases with respect to the contribution of the 3.7 eV band when excited at 5.6 eV. The time decays of the two bands excited at 5.6 eV were fitted with two exponential decays with mean life times of about 2.6 and in the range 20–60 ns for the 2.8 eV emission and 2.6 and 21.8 ns for the 3.7 eV emission. The analysis of the spectroscopic features suggests the attribution to different emitting surface centers and the presence of at least two contributions for both the emissions. We assign the 3.7 eV band to two different species of interacting silanols.

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.

In this paper, we investigate the kinetics of photoluminescence in excited crystals of HgGa2S4 which have recently been proposed for implementing tunable luminescent devices. From photoluminescence experiments, performed at various temperatures and excitation powers, it appears that two kinds of radiative recombination processes take place during crystal excitation. These originate two bands in emission spectra which were resolved by means of a fitting procedure. The dependencies of these bands on temperature and excitation power density are explained by means of a specific kinetic model. A broad band, peaking at about 1.8 eV, is ascribed to electron–hole tunnel recombinations occurring in associated donor–acceptor pairs, according to a Prener–Williams scheme. The second narrow band, peaking at about 2.3 eV, is ascribed to electron–hole recombinations occurring in centres presenting short ( ∼ 10 - 8 s ) and long-life ( ∼ 10 - 6 s ) excited states. At room temperature, owing to thermally activated relaxation from short- to long-life states, these centres saturate under relatively low excitation powers. The tunability of photoluminescence is a consequence of competition between monomolecular and bimolecular recombination processes.

The optical properties of porous silica were studied by means of synchrotron radiation. We investigated the spectral properties of the blue photoluminescence band as a function of the porosity of the samples. In the whole set of samples the blue band is centered at about 2.8 eV, with main excitations at 5.0 and 6.0 eV. Time decay analysis indicates the contemporary presence of two contributions of photoluminescence.

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.

Ultraviolet excited photoluminescence of porous silica under vacuum conditions is investigated in samples with different pore diameters. By exciting in the 180–300 nm range, a manifold luminescence activity in the 300–600 nm is found. The reconstructed three-dimensional photoluminescence excitation pattern shows how the distribution of the emissions changes by varying the pore size of the samples. Two different centers are singled out and their relative concentration is suggested to be a function of the pore size of the samples.

Mercury thiogallate, HgGa 2 S 4 is a defect chalcopyrite semiconductor with the space group S 4 2 which offers a combination of attractive properties for applications. In order to obtain information about the electron states in the energy gap, photoconductivity measurements are performed in the 80–300 K range. Photoconductivity spectra show two peaks related to intrinsic and extrinsic excitation at about 410 and 500 nm, respectively; these maxima show a temperature dependence similar to the linear coefficient of the energy gap. Thermally stimulated currents have been studied by exciting the samples with intrinsic light at different temperatures. For all excitation temperatures a single TSC peaks were obtained. The analysis of TSC curves allowed one to estimate the kinetics of the trap emptying, trap energy distribution and thermal activation energy. A model for the level distribution in the semiconductor energy gap is suggested which in good agreement with the results of a previous photoluminescence study.

Mercury thiogallate single crystals are shown to exhibit bright photoluminescence (PL) tunable in a wide spectral range from green to red when changing the excitation power density, wavelength and sample temperature. Taking into account the excitation and temperature dependencies of the PL characteristics, a model accounting for the radiative electron transitions in HgGa2S4 is proposed. The values of the energy gap extrapolated to 0 K and of the linear and quadratic temperature coefficients of the energy gap [ Eg (0)=2.997 eV ; a=−1.34×10 −4 eV K −1 ; b=−1.29×10 −6 eV K −2 ] were deduced from PL excitation experiments.

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.

Forty patients with unilateral frontal or posterior brain damage and 20 normal control subjects were tested on an ambiguous figures task (AFT). For each figure they were asked to recognize both ambiguous images. Subjects failing to recognize the second aspect of an ambiguous figure were prompted with the name of the image not yet perceived. The Wisconsin Card Sorting Test (WCST) was also administered to all subjects. Frontal patients exhibited greater difficulty in shifting from one aspect of an ambiguous figure to the other than did patients with more posterior lesions and control subjects. In addition, frontal-posterior and control differences were highly significant for number of prompts given. For the frontal patients, significant correlations were found between the number of prompts on the AFT and the number of perseverative errors on the WCST. Poor performance on the AFT can be considered as a “frontal lobe sign” of perceptual perseveration.

Corrigendum to “Optical properties of sol gel prepared Cerium doped Lutetium and Yttrium oxyorthosilicates” [Journal of Non–Crystalline Solids 357 (8–9) (2011 April 15) 1908–1911] P.C. Ricci , C.M. Carbonaro⁎, L. Stagi , A. Anedda, F. Ferrari , D. Capsoni , A. Magistris c a Dipartimento di Fisica, Universita di Cagliari, s.p. n 8 Km 0.700, 09042 Monserrato, Cagliari, Italy b Centro Grandi Strumenti Universita di Cagliari, s.p. n 8 Km 0.700, 09042 Monserrato, Cagliari, Italy c Dipartimento di Fisica Chimica, Universita di Pavia, V.leTaramelli 16, I-27100 Pavia, Italy