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Lead halide perovskite materials have outstanding optical properties such as color purity and efficient fluorescence in the visible spectrum. However, the toxicity of lead makes the synthesis, processing, use and disposal of such materials hazardous for humans and the environment. Therefore, the exploration of different perovskite materials containing the transition metal Mn(II) and fluoride anions might lead to more appealing alternatives towards more sustainable and environmentally friendly functional materials. Nanocrystals primarily consisting of cubic CsMnF3 - a polymorph so far only reported at pressures of 3 x 10(4 )bar - were synthesized from manganese(II) acetate and caesium fluoride precursors using a heating-up approach in high boiling organic solvents. The concentration of defects could be tuned by changing the amount of fluorinating precursor CsF, with more defects produced when an excess of CsF was used in the synthesis. The structure, morphology, optical and magnetic properties of the product nanoparticles were studied. Due to their X-ray sensitized fluorescence, likely caused by defects in the crystal structure, these materials are promising for potential applications in dosimetry., Journal of Sol-Gel Science and Technology, ISSN:0928-0707, ISSN:1573-4846

Hafnium-based halide crystals are attractive wide-bandgap phosphor materials for scintillation applications due to their high density, low hygroscopicity and bright radioluminescence. Here, we describe synthetic approaches towards the formation of Cs2HfCl6 (CHC) microparticles and Cs2HfF6 (CHF) nanocrystals. The structure of the obtained materials was characterised by means of powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surface chemistry was studied by attenuated total reflection infrared spectroscopy (ATR-IR) and dynamic light scattering (DLS) while thermal properties were determined with thermogravimetric analysis (TGA). The optical properties of the products were elucidated through absorption (UV-vis) and photoluminescence (PL/PLE) spectra. Intrinsically luminescent CHC can be synthesised as a micropowder through an emulsion synthesis. The synthesis of pure and Eu- or Mn-doped CHF nanopowders in organic solvents at 160 degrees C and atmospheric pressure is also disclosed. These materials might pave the way towards the versatile additive manufacturing of lead-free and dopant-free, particle-based scintillator materials., Journal of Materials Chemistry C, 10 (11), ISSN:2050-7526, ISSN:2050-7534

Synthetic procedures to obtain size and shape-controlled microparticles hold great promise to achieve structural control on the microscale of macroscopic ceramic- or composite-materials. Lutetium oxide is a material relevant for scintillation due to its high density and the possibility to dope with rare earth emitter ions. However, rare earth sesquioxides are challenging to synthesise using bottom-up methods. Therefore, calcination represents an interesting approach to transform lutetium-based particles to corresponding sesquioxides. Here, the controlled solvothermal synthesis of size-tuneable europium doped Lu(OH)(2)Cl microplatelets and their heat-induced transformation to Eu:Lu2O3 above 800 degrees C are described. The particles obtained in microwave solvothermal conditions, and their thermal evolution were studied using powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy, thermogravimetric analysis (TGA), luminescence spectroscopy (PL/PLE) and infrared spectroscopy (ATR-IR). The successful transformation of Eu:Lu(OH)(2)Cl particles into polycrystalline Eu:Lu2O3 microparticles is reported, together with the detailed analysis of their initial and final morphology., Crystals, 11 (8), ISSN:2073-4352

Luminescent nanoparticles are researched for their potential impact in medical science, but no materials approved for parenteral use have been available so far. To overcome this issue, we demonstrate that Eu3+-doped hafnium dioxide nanocrystals can be used as non-toxic, highly stable probes for cellular optical imaging and as radiosensitive materials for clinical treatment. Furthermore, viability and biocompatibility tests on artificially stressed cell cultures reveal their ability to buffer reactive oxygen species, proposing an anti-cytotoxic feature interesting for biomedical applications.

Titanium dioxide (TiO2) nanoparticles were synthesized by nonaqueous sol–gel route using titanium tetrachloride and benzyl alcohol as the solvent. The obtained 4 nm-sized anatase nanocrystals were readily dispersible in various polar solvents allowing for simple preparation of colloidal dispersions in water, isopropyl alcohol, dimethyl sulfoxide, and ethanol. Results showed that dispersed nanoparticles have acidic properties and exhibit positive zeta-potential which is suitable for their deposition by cathodic electrophoresis. Aluminum substrates were anodized in phosphoric acid in order to produce porous anodic oxide layers with pores ranging from 160 to 320 nm. The resulting nanopores were then filled with TiO2 nanoparticles by electrophoretic deposition. The influence of the solvent, the electric field, and the morphological characteristics of the alumina layer (i.e., barrier layer and porosity) were studied.

Bulk materials with remarkable mechanical properties have been developed by incorporating design principles of biological nacre into synthetic composites. However, this potential has not yet been fully leveraged for the fabrication of tough and strong materials that are also optically transparent. In this work, a manufacturing route that enables the formation of nacre‐like mineral bridges in a bioinspired composite consisting of glass platelets infiltrated with an index‐matching polymer matrix is developed. By varying the pressure applied during compaction of the glass platelets, composites with tunable levels of mineral bridges and platelet interconnectivity can be easily fabricated. The effect of platelet interconnectivity on the mechanical strength and fracture behavior of the bioinspired composites is investigated by performing state‐of‐the‐art fracture experiments combined with in situ electron microscopy. The results show that the formation of interconnections between platelets leads to bulk transparent materials with an unprecedented combination of strength and fracture toughness. This unusual set of properties can potentially fulfill currently unmet demands in electronic displays and related technologies., Advanced Functional Materials, 30 (27), ISSN:1616-3028, ISSN:1616-301X

International audience; The recent trends in scintillator technologies stimulate research efforts toward the development of novel materials morphologies, such as nanoparticles, able to efficiently convert ionizing radiations into light. For example, scintillating nanoparticles attract great interest in medical oncological therapies. In this work, the structural and morphological properties of HfO2:Ti nanoparticles with Ti concentrations from 0.03 to 10 mol% and subjected to calcination up to 1000 °C are thoroughly characterized; moreover, X‐ray photoelectron spectroscopy reveals the incorporation of Ti in both Ti (III) and Ti (IV) chemical states in as prepared samples, while the exclusive presence of Ti(IV) is unambiguously identified in calcined nanoparticles. The optical emission under X‐ray excitation evidences an intense Ti (IV)‐related luminescence at 2.5 eV in high temperature calcined samples with a few microseconds scintillation lifetime, and efficiency comparable to that of Bi4Ge3O12 reference scintillator. Finally, the competitive role of defects in charge carriers capture is demonstrated by the monotonic increase of the 2.5 eV band during prolonged X‐ray irradiation, more evident for nanoparticles with titanium concentration below 1 mol%. HfO2:Ti may also find application in X‐ray triggered oncological therapies by using the Ti (IV)‐related bright radioluminescence to excite photosensitizer molecules for singlet oxygen generation.

Defect engineering operated on metal oxides by chemical and structural modifications may strongly affect properties suitable for various applications such as photoelectrochemical behavior, charge transport, and luminescence. In this work, we report the tunable optical features observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time-resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with a decay time of a few nanoseconds) overlaps with a slower emission (decay of several microseconds) due to extrinsic Ti-impurity centers. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modeled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at crystal boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO2 under near-UV excitation.

Here a sustainable approach for the bottom-up fabrication of luminescent carbon dots (CDs) through a green synthetic route by using polymeric waste as a single precursor material is developed. Polylactide has been selected as a carbon-containing model polymeric waste because of its remarkable presence in the packaging field and its associated “white-pollution”. Spherical CDs with diameters of 3 nm have been synthesized through a one-pot hydrothermal reaction of water-dissolved polylactide oligomers (Mn = 1.200–1.900 g mol−1) at mild temperatures. Chemical, structural, morphological and optical properties of the synthesized CDs have been studied. Results reveal that CDs consist of a carbonaceous nucleus having a sp2 conformation with carboxyl and hydroxyl surface groups, making it dispersible in polar media. The optical features of obtained CDs depend on reaction conditions (time and temperature) and on the insertion of nitrogen groups within the CD structure. A proof of concept study of the application of the proposed approach for the production of luminescent CDs from commercial PLA lids for paper hot cups is also provided. The route here reported provides novel cues for a catalyst-free and organic-solvent-free industrial-scale fabrication of photoluminescent nanomaterials from actual polymeric waste as a viable non-toxic and cheap alternative to quantum dots and rare earth based nanophosphors.

Materials combining optical transparency and mechanical strength are highly demanded for electronic displays, structural windows and in the arts, but the oxide-based glasses currently used in most of these applications suffer from brittle fracture and low crack tolerance. We report a simple approach to fabricate bulk transparent materials with a nacre-like architecture that can effectively arrest the propagation of cracks during fracture. Mechanical characterization shows that our glass-based composites exceed up to a factor of 3 the fracture toughness of common glasses, while keeping flexural strengths comparable to transparent polymers, silica- and soda-lime glasses. Due to the presence of stiff reinforcing platelets, the hardness of the obtained composites is an order of magnitude higher than that of transparent polymers. By implementing biological design principles into glass-based materials at the microscale, our approach opens a promising new avenue for the manufacturing of structural materials combining antagonistic functional properties., Nature Communications, 10 (1), ISSN:2041-1723

Although solvent-ligand interactions play a major role in nanocrystal synthesis, dispersion formulation, and assembly, there is currently no direct method to study this. Here we examine the broadening of 1H NMR resonances associated with bound ligands and turn this poorly understood descriptor into a tool to assess solvent-ligand interactions. We show that the line broadening has both a homogeneous and a heterogeneous component. The former is nanocrystal-size dependent, and the latter results from solvent-ligand interactions. Our model is supported by experimental and theoretical evidence that correlates broad NMR lines with poor ligand solvation. This correlation is found across a wide range of solvents, extending from water to hexane, for both hydrophobic and hydrophilic ligand types, and for a multitude of oxide, sulfide, and selenide nanocrystals. Our findings thus put forward NMR line-shape analysis as an indispensable tool to form, investigate, and manipulate nanocolloids.

Although solvent-ligand interactions play a major role in nanocrystal synthesis, dispersion formulation and assembly, there is currently no direct method to study this. Here we examine the broadening of 1H NMR resonances associated with bound ligands, and turn this poorly understood descriptor into a tool to assess solvent-ligand interactions. We show that the line broadening has both a homogeneous and a heterogeneous component. The former is nanocrystal-size dependent and the latter results from solvent-ligand interactions. Our model is supported by experimental and theoretical evidence that correlates broad NMR lines with poor ligand solvation. This correlation is found across a wide range of solvents, extending from water to hexane, for both hydrophobic and hydrophilic ligand types, and for a multitude of oxide, sulfide and selenide nanocrystals. Our findings thus put forward NMR line shape analysis as an indispensable tool to form, investigate and manipulate nanocolloids.

International audience; In this work, we investigate the optical properties of hafnium dioxide nanocrystals, upon X-ray irradiation, looking for spectral evolution following thermal treatments in air up to 1000 °C that modify the crystal size as well as their point defect concentrations. Radio-luminescence measurements from 10 K up to room temperature reveal a rich and evolving picture of the optical features. A complete spectral analysis of the broad luminescence spectra reveals the presence of several emission components in the visible and UV regions. The lower energy components peaking at 2.1, 2.5, and 2.9 eV are characterized by a thermal quenching energy of 0.08 eV, while the corresponding value for the UV bands at 4.1 and 4.7 eV is close to 0.23 eV. We tentatively assign the components ranging from 2 to 3 eV to the presence of optically active defects of an intrinsic nature, together with the occurrence of titanium impurities; conversely, the bands at higher energies are likely to be of an excitonic nature. The comparison with previous photo-luminescence studies allows evidencing characteristic differences between the features of luminescence emissions caused by intra-centre excitation and those occurring under ionizing irradiation. Finally, scintillation measurements in the visible range reveal the existence of a fast decay in the nanosecond time scale for the smallest hafnia nanocrystals. This study offers a clear description of HfO2 luminescence characteristics upon excitation by X-rays and can lead to a better comprehension of the structure–property relationship at the nanoscale in metal oxides.

The problem of Eu incorporation into silica as dispersed dopants, clusters, separate-phase nanoparticles, or nanocrystals, which is of key importance for applications in the fields of lasers and scintillators, is faced by applying to sol−gel silica doped with nine different Eu3+ concentrations (0.001−10 mol % range) various spectroscopic techniques, including crystal field and vibrational mode analysis by means of Fourier transform absorption and microreflectivity (in the 200−6000 cm−1 and 9−300 K ranges), radioluminescence, and Raman scattering studies at 300 K. The variety of methods revealed the following concordant results: (1) amorphous Eu clusters grow when the Eu concentration is increased up to 3 mol % and (2) Si−OH groups are completely removed and ordered phase separation occurs at 10 mol % doping, as suggested by the remarkable narrowing of the spectral lines. Comparison with polycrystalline Eu oxide, Eu silicates, and α- quartz spectra allowed the unequivocal identification of Eu2Si2O7 pyrosilicate and α-quartz as the main components of nanocrystals in 10 mol % Eu-doped silica. Such conclusions were brilliantly confirmed by transmission electron microscopy and electron diffraction analysis. Phonon coupling and anharmonicity were analyzed and are discussed for a few vibrational modes of nanocrystals.

The fundamental mission of materials science is the description of matter over all length scales. In this review, we apply this concept to particle research. Based on metal oxides, we show that every size range offers its specific features, and every size range had its era, when it was in the center of the research activities. In the first part of the review, we discuss on three metal oxides as examples, how and why the research focus changed its targeted size regime from the micrometer to the nanometer scale and back to the macroscopic world. Next, we present the distinct advantages of using nanoparticles over micrometer-sized particles in selected devices and we point out how such a shift in the size regime opens up new research directions. Finally, we exemplify the methods to introduce nanoparticles into macroscopic objects to make functional ceramics.

In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu3+ or Eu3+. The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu3+ luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu3+ ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders. © 2013 American Chemical Society.

Section Analysis, line 9: sub-sample of 818 events becomes sub-sample of 817 events., 0, SCOPUS: er.j, info:eu-repo/semantics/published

Fluorinated silica glasses with improved vacuum ultraviolet (VUV) transmittance have been synthesized following a sol-gel route starting from fluorinated alkoxide precursors. Matrix dehydration and fluorination have been investigated by Raman, IR, and refractive index measurements. The results show that, during the densification step, the residual hydroxyl and fluorine content can be controlled by governing the kinetic equilibrium between matrix collapse and fluorine evolution. This highlights the pivotal role of in situ reactions of fluorine-containing molecular precursors in the networking mechanism of a sol-gel material after thermal activation. Superior VUV transmittance and radiation hardness with respect to pure commercial silica and undoped sol-gel silica have been confirmed by synchrotron light absorption measurements before and after X-ray exposure. These properties make the material very attractive for applications in VUV photolithography technologies and optical fibers, especially for use in environments with a high level of ionizing radiation, such as spacecrafts and nuclear power plants.

Structural and optical properties of sol–gel silica based glassceramics doped with 0.1 mol% Ce and codoped with Gd at high concentrations, from 5 mol% up to 40 mol%, are investigated and compared to those of analogous samples doped only with Ce. Raman scattering, transmission electron microscopy, and x-ray diffraction reveal the formation of Gd apatite-like silicate (Gd4.67O(SiO4)3) and of Gd pyrosilicate (Gd2Si2O7) nanophases whose morphology and crystallinity depend on the Gd concentration and thermal treatments. Optical absorption measurements demonstrate the role of the densification atmosphere in modifying the charge state of Ce ions. The incorporation of Ce3+ ions in the nanophases is put in evidence by photo- and radio-luminescence results.

We measured temperature dependences of emission spectra, prompt nanosecond decays and millisecond delayed recombination decays for the Ce3+ center in the SrHfO3 (SHO) host. We characterized two samples with 0.1% and 5Î prepared by the acetate and citrate combustion and solid state reaction, respectively. The decrease of nanosecond decay times above approximately 220 and 260 K, respectively, is due to thermal ionization of 5d1 excited state of the Ce3+ center. Energy barrier of 300 meV, governing this process, is calculated for both the 0.1% and 5Î:SHO samples. Thermoluminescence glow curve measurement after X and UV (310 nm) irradiation at RT provides another support for the 5d1 excited-state ionization of Ce3+ in the SHO host. © 2010 Elsevier B.V. All rights reserved.

Host-tissue integration of medical implants is governed by their surface properties. The capacity to rationally design the surface physico-chemical cues of implantable materials is thus a fundamental prerequisite to confer enhanced biocompatibility. Our previous work demonstrated that different cellular processes are elicited by the nanotexture generated on titanium (cpTi) and Ti6Al4V alloy by chemical oxidation with a H2SO4/H2O2 mixture. Here, we illustrate that by varying the etching parameters such as temperature, concentration, and treatment time, we can create a variety of surface features on titanium which are expected to impact its biological response. The modified submicron and nanotextured surfaces were characterized by scanning electron (SEM) and atomic force (AFM) microscopies. Contact angle measurements revealed the higher hydrophilicity of the modified surfaces compared to untreated samples and Fourier transform infrared spectroscopy (FT-IR) established that the etching generated a TiO2 layer with a thickness in the 40–60 nm range.

The effect of sintering atmosphere on the optical and structural properties of Cerium doped sol-gel silica was investigated. Two sets of xerogels with Ce concentration from 0 to 10 mol% were prepared and densified in different conditions. The effect of a post-densification rapid thermal treatment was also considered. Optical absorption measurements evidenced that in oxidizing conditions Cerium is preferably incorporated inside the silica matrix as Ce4+ while the trivalent state is favoured by reducing conditions. Transmission electron microscopy images show rare-earth clusters formation whose nature was investigated by means of Raman, EDS and microdiffraction measurements. In order to evaluate the efficiency of the glasses as scintillating materials radio-luminescence measurements were carried out. A numerical fit of RL spectra showed the presence of two components peaking at 2.7 and 3.1 eV. After RTT, the relative intensity of the 3.1 eV component increases with Ce concentration. © 2009 Elsevier B.V. All rights reserved.

Elemental Ge nanophases are obtained in silica starting from a sol-gel synthesis. The process comprises the preparation of silica xerogel doped by Ge(IV), substituting for Si(IV) in the oxide network, followed by reduction and phase separation during the sintering process by reaction with H-2 or CO. X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy show that reactions with H-2 give rise in the porous silica network to nanometer-sized crystallization of elemental cubic germanium. (c) 2007 Elsevier Ltd. All rights reserved.

We show here what kind of modification of the interphase morphology of SnO2 nanoparticles in silica (average nanocrystal radius, \(\hat{r}\approx 4\,\hbox{nm}\) in undoped material; \(\hat{r}\,\approx\,2\,\hbox{nm}\) in erbium doped material) brings to the passivation of interfacial defects. Surface states, which may preclude the exploitation of UV excitonic emission, are reduced after doping by rare earth ions. We demonstrate, by means of transmission-electron-microscopy and small-angle-neutron-scattering data, that a smooth interphase with a non negligible thickness takes the place of the fractal and discontinuous boundary observed in undoped material.

A set of terbium-doped silicate glasses densified up to 1050 °C was prepared by the sol-gel method. A broad range of dopant concentrations (0.001-10 mol%) was considered together with an undoped sample as a reference. The effects of a high-temperature (1600-1800 °C) post-densification rapid thermal treatment (RTT) on the luminescence properties of the samples were investigated. RTT enhances the scintillating efficiency of the samples increasing the radio-luminescence intensity up to two orders of magnitude. The relevant effects induced by RTT on radio- and photo-luminescence spectra (RL, PL) and on PL decay curves indicate the occurrence of modifications of the surroundings of Tb3 + luminescence centres. © 2007 Elsevier Ltd. All rights reserved.

The energy levels belonging to the three lowest J multiplets of the Er3+ ion in Er2O3 and ErF3 were determined by means of high-resolution optical absorption spectroscopy. A crystal-field analysis of these data by means of Newman's Superposition Model was performed, allowing to determine intrinsic parameters which are quite consistent with other oxides and fluorides and to check the validity of the transferability postulate within these compounds. The possibility to use these data to analyze crystalline nanophases in glasses is briefly discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Radiation-induced spectral modifications of the 5 eV excited photoluminescence (PL) of oxygen vacancies have been found in a nanostructured silica-based material. This system, made up of SnO2 nanocrystals embedded in amorphous SiO2, is generated by nano-clustering in oversaturated Sn-doped silica produced by sol-gel method. Treatment in oxygen-poor atmosphere introduces oxygen deficiency in the glassy host and a photo-reactive SnO-like interphase at the SnO2 nanocrystal surface. PL measurements initially show native PL activity at 2.7 eV excited at 5 eV, ascribable to oxygen vacancies in intrinsic two-fold coordinated Si sites. Prolonged UV irradiation at 4.7 eV (fourth harmonic of Nd-YAG pulsed laser) gives rise to extrinsic PL activity at 3.1 eV, ascribable to Sn-variant of oxygen vacancy. The results suggest that the UV irradiation causes a progressive release of Sn from the nanophase surface to the glassy network in oxygen vacancy sites. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

We investigate the effects of erbium doping on SnO(2) nanoclustering in Sn-doped silica. Vibrational spectroscopy data from Raman and infrared absorption measurements show nanostructuring effects on the SnO(2) nanophase. Ultraviolet absorption spectra evidence a gap shift ascribable to size-dependent quantum confinement, also suggesting a role of erbium doping in determining cluster sizes and the amount of localized states on the nanophase boundary. Transmission electron microscopy confirms and details the spectroscopic data. As a result of these measurements, we find that the nanocrystal size distribution becomes narrower, increasing the erbium concentration, while the density of localized states at the nanocrystal surface decreases. The distribution of erbium ions among the possible environments is then examined through simultaneous spectroscopy of luminescence excited by nanocrystal-to-erbium energy transfer and the absorption of nanocrystal luminescence by erbium ions. This analysis shows that erbium behaves as an extrinsic nucleation centre of the SnO(2) nanophase at low doping levels, whereas at high concentrations it modifies the matrix, hindering the growth of SnO(2) crystals and passivating the interface.

Thermal poling has been investigated in silica-based glasses prepared by the sol-gel method. Samples with different OH-content (from 40 ppm to few 10(3) ppm), doping (oxygen-vacancies, substitutional Sn, SnO2 clusters) and post-synthesis treatment (X-ray irradiation) have been heated in vacuum at 280 degrees C with an applied voltage of 4 kV. Second-order non-linearity has been observed after poling, with chi((2)) of the order of 0.1 pm/V. The comparison among samples suggests that OH-content is not the only factor responsible for the observed non-linearity. (C) 2005 Elsevier Ltd. All rights reserved.

Sn-doped silica and SnO2:SiO2 glass-ceramics were produced by sol-gel synthesis. Charge trapping and radiative recombinations from ionizing irradiation were investigated in the 8-300 K range. Three radioluminescence (RL) emissions were observed at 1.9, 2.3 and 3.2eV. Dose-dependence of RL shows that the 3.2eV emission grows during the irradiation. 2.3eV RL is the main process at low temperature, whereas it is a minor decay at 300K, as well as in phosphorescence and thermoluminescence. Glow curves show peaks at 80 and 200K. The results suggest that radiative decays and trapping processes occur in the silica network. © 2004 Elsevier B.V. All rights reserved.

We present a novel strategy for the synthesis of pure and Eu-doped γ-Ga2O3 nanoparticles with an in situ organic capping resulting from a non-aqueous solution-based benzyl alcohol synthesis route. Photoluminescence spectroscopy highlights the concomitant benzoate-related and γ-Ga2O3 exciton-like Eu3+ excitations in the UV, and a blue emission superimposed onto γ-Ga2O3 donor–acceptor recombination, ascribable to organic moieties different from benzoate.

We study trapping states of Ce 3+ -doped SrHfO 3 by thermally stimulated luminescence in a wide temperature range (10–730 K). We determine characteristic parameters of the traps by the initial rise technique. We also determine the energy of thermal ionization of the excited state of Ce 3+ in SrHfO 3 host by purely optical method based on the study of UV illumination-induced thermoluminescence. The method provides a value of the thermal ionization energy of about 0.25 eV.

The development of integrated photonics and lab-on-a-chip platforms for environmental and biomedical diagnostics demands ultraviolet electroluminescent materials with high mechanical, chemical and environmental stability and almost complete compatibility with existing silicon technology. Here we report the realization of fully inorganic ultraviolet light-emitting diodes emitting at 390 nm with a maximum external quantum efficiency of ~0.3%, based on SnO(2) nanoparticles embedded in SiO(2) thin films obtained from a solution-processed method. The fabrication involves a single deposition step onto a silicon wafer followed by a thermal treatment in a controlled atmosphere. The fully inorganic architecture ensures superior mechanical robustness and optimal chemical stability in organic solvents and aqueous solutions. The versatility of the fabrication process broadens the possibility of optimizing this strategy and extending it to other nanostructured systems for designed applications, such as active components of wearable health monitors or biomedical devices.

We present the results of the analysis of the ultraviolet (UV) absorption edge of fluorine-modified sol-gel silica. UV transmission data, obtained by means of synchrotron radiation, have been analyzed in the spectral range 7.5–8.5 eV, with a spectral resolution of about 10 meV. Data on silica samples with different F content (from 0 to few 10 − 1 mol%) have been analyzed and compared with literature data on quartz and pure synthetic commercial silica. The analysis allows us to discriminate between the effects of the fluorine addition and those ascribable to structural peculiarities of the sol-gel networking. The estimated Urbach energy E U ( T = 0) ranges between 45 and 55 meV, higher that in crystalline quartz and lower than in commercial synthetic silica. The study of the temperature dependence of E U ( T ) shows that the fluorine modification of the silica network causes the lowering of the static disorder and the widening of the energy gap. However, there is also a relevant effect of the production process, since sol-gel silica samples show lower E U values with respect to other types of silica, quite independently of the fluorine content. The analysis of the Raman spectra however shows that the starting amount of fluorine-modified molecular precursor influences the network condensation process, independently of the final fluorine content into the matrix.

Silica thin films with embedded SnO 2 nanoparticles have been grown on transparent substrates by the sol–gel method. Tin dioxide crystals with cassiterite structure are semiconductors with a wide band gap of ~ 3.6 eV. Optical absorption spectroscopy in the near ultraviolet–visible range has been exploited to probe nanostructuring features of such nanocrystals. The results show that the sintering conditions modify crystallite mean size and enable the occurrence of quantum confinement effects. The outcome is in accordance with transmission electron microscopy data conducted on analogous bulk samples.

We study lutetium hafnate, Lu4Hf3O12, prepared by acetate and citrate combustion in the form of nanometric powders. Optical properties including X-ray excited luminescence, steady-state and time resolved photoluminescence as well as thermally stimulated luminescence are investigated for undoped as well as Eu3+ and Tb3+ doped samples. We identify recombination centers in the host matrix and we tentatively associate the principal emission with a radiative transition of the F + center. We also demonstrate that athermal tunneling of charge carriers between traps and recombination centers is the predominant mechanism of delayed radiative recombination following irradiation by ionizing radiation. © 2011 Elsevier B.V. All rights reserved.

To better understand the scintillation mechanism in SrHfO3-based scintillators we investigate in detail their x-ray excited radioluminescence (RL) emissions. The Gaussian decomposition of the undoped SrHfO3 RL spectra manifests the presence of four emission bands peaking at 3.0, 4.0, 4.6, and 5.1 eV. Based on corresponding photoluminescence emission and excitation spectra we tentatively associate the observed bands with excitonic or defect-related emissions. When doped by Ce3+ or Pb2+ luminescent activators, the RL spectra feature two or three new bands, respectively. The temperature dependence of all RL spectra demonstrates a competition between activators and intrinsic or defect centers in carrier capture. Around room temperature the emission process is completely dominated by recombination at activator centers. In the case of Pb2+ activator we also study in detail the concentration dependence of the RL spectra below room temperature exhibiting an optimal value around 0.3 mol %.

We use acetate–citrate combustion to prepare SrHfO3 powders both undoped and doped with Ce3+ and Pb2+ ions in several concentrations, from 0.01 up to 3 mol%. The evolution of their morphological and structural features during the sintering process is studied by scanning electron microscopy, X-ray diffraction, and Raman experiments. We discuss the dependence of the optical properties, investigated by radioluminescence and time resolved luminescence, on sintering conditions and material structure.

We bring into consideration a novel, potentially promising scintillating material, Pb-doped SrHfO3. The structural and optical properties of a series of Pb-doped SrHfO3 powders prepared by acetate and citrate combustion are investigated and compared to those of undoped and Ce-doped powders with the same composition. Room temperature radioluminescence studies as a function of sintering temperature show that samples sintered up to the highest final temperature (1150 degrees C) display the highest light output. Moreover, Pb-doped SrHfO shows a higher radioluminescence efficiency with respect to Ce-doped SrHfO3, which in turn features a very fast photoluminescence decay time of 15 ns. The presence of point defects and their role in carrier trapping are studied by thermally stimulated luminescence as well as by radioluminescence as a function of temperature.

In the present work the effects produced by Eu3+ incorporation into sol-gel silica (doping level range: 0.001-10 mol%) are monitored by means of Fourier transform vibrational spectroscopy in the wave number range 200-3000 cm(-1). Complementary microreflectance, TEM, and Raman spectroscopy measurements are also performed. By increasing the Eu3+ concentration up to 3 mol%, the intrinsic absorption/reflectance bands related to vibrational modes of O-Si-O groups are gradually modified for what concerns the peak position and intensity, and absorption shoulders attributable to the Eu3+ doping appear. At 10 mol% sharp, new, Eu-related peaks grow at the expenses of the intrinsic absorptions. The results can be explained in terms of Eu-rich cluster formation, as also supported by Raman spectra analysis and TEM images. The cluster sizes increase by increasing the Eu3+ concentration. Their structure, in which tetrahedral (SiO4)(4-) groups are still present, remains amorphous for Eu3+ concentration up to 3 mol%, turning into a nearly ordered arrangement for the higher one. The spectral analysis in the regions of the weaker absorptions due to combination and overtone modes further supports the results and allows to associate the fundamental and overtone frequencies for two modes in Eu3+ 10 mol% doped silica. In the framework of the Morse anharmonic oscillator model, the related anharmonicity parameters and binding energies were calculated and found close to those reported for (SiO4)(4-) groups.

S. Brovelli,1,2 N. Chiodini,1 F. Meinardi,1 A. Monguzzi,1 A. Lauria,1 R. Lorenzi,1 B. Vodopivec,1 M. C. Mozzati,3 and A. Paleari1 1CNISM–Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy 2London Centre for Nanotechnology, and Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom 3CNISM–Department of Physics “Alessandro Volta,” University of Pavia, via Bassi 6, I-27100 Pavia, Italy Received 19 January 2009; published 24 April 2009

Photoluminescence in fluorine-modified Sn-doped silica has been analyzed by means of synchrotron radiation in the UV and vacuum-UV, from 120 to 330 nm, looking at the optical activity of oxygen-deficient-centers ODC(II) in Sn-substituted cationic sites. The comparison between F-modified Sn-doped samples and previous data on F-free Sn-doped material evidences differences in the intensity of the 3.2 eV emission band excited at 3.7 eV, and in the thermal dependence of the intensity of this emission excited via intersystem crossing. The role of fluorine in modifying the optical activity of ODC(II) and in the SnO2 clustering is discussed, showing that an efficient excitation transfer may be activated from SnO2 to the Sn-variant of ODC(II). © 2009 Elsevier B.V. All rights reserved.

Silica samples with embedded SnO2 nanoparticles have been produced by sol-gel method with a synthesis modified by the introduction of fluorinated silicon precursors. The structural features of silica network and SnO2 nanophase have been mapped inside the samples by means of confocal micro-Raman scattering spectroscopy. The results show that the detection of residual fluorine into the matrix as Si-F groups is accompanied by network dehydration, by intensity depletion of the D2 peak assigned to three-member rings of coordinated tetrahedra, and by SnO2 nanoparticles with much larger sizes than in fluorine-free material. © 2009 Elsevier B.V. All rights reserved.

Silica xerogels doped with Ge(IV), substituting for Si(IV) in the oxide network, are prepared from tetraethylorthosilicate and germanium-tetraethoxide. The sintering process is carried out in reducing atmosphere at 700 - 900° C by reaction with H 2 . Raman spectroscopy and high resolution transmission electron microscopy (TEM) show that reactions with H 2 give rise, in the porous silica network, to uncontrolled islands of crystallites of elemental cubic germanium with average size of 50 nm. Sintering process in reducing H 2 atmosphere at temperatures just below the phase separation, at about 610°C, gives materials where Ge atoms are dispersed in the matrix in conditions of incipient clustering. Evidences of segregation of germanium nanocrystals are observed with electron irradiation during TEM analysis. Furthermore, the electron beam induced precipitation leads to the formation of isolated quantum dots-like nanocrystals (5-6 nm in diameter) and with narrower size dispersion. The ranges of suitable temperature and germanium concentration are analysed, as well as the size dispersion of the resulting Ge nanophases.