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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

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

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.

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

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.

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.

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 %.

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

We show that Sn O2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10-2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology. © 2006 American Institute of Physics.

A radioluminescent (RL) dosimetric system, based on a SiO2 optical fiber with the core doped by Ce3+ ions as luminescent activators has been investigated. Structural and optical properties of the luminescent fiber have been studied by Raman, refractive index, RL and scintillation time decay measurements, and compared to those obtained on bulk material. The RL response of a composite fiber made of a short portion of active Ce-doped fiber coupled to a long commercial one has been investigated by x-ray irradiation. A linear RL intensity response has been found in the dose rate interval 6x10(-3)-40 mGy/s together with a good radiation hardness, suggesting possible application in low-dose monitoring. (C) 2004 American Institute of Physics.

Fluorine modified amorphous silica has been synthetized via sol-gel route and studied through analysis of the temperature dependence of the Urbach absorption tail in the vacuum-ultraviolet region. The modified glass has a steep absorption edge above 8 eV, with the absorption coefficient alpha proportional to exp[E/E-U(T)] showing Urbach energy values E-U(T) ranging between 50 and 66 meV. The comparison of E-U(T) with pure silica data indicates a structural softening caused by the reduction of dynamical disorder, and suggests that the F-modified sol-gel synthesis is an appropriate route for achieving high energy shifts of the absorption edge. (C) 2007 American Institute of Physics.

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