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Air-stable Ni nanoparticles (with particle size ∼ 11 nm) supported on reduced graphene oxide [Ni(0)@RGO] was prepared by a simple and easy procedure. We previously described the Kumada-Corriu C-C cross-coupling reaction between iodo-arenes and Grignard reagents with Ni(0)RGO as a stable and efficient catalyst. This Ni(0)RGO catalyst gave an excellent yield (92%) and good recyclability (up to the 5

Transparent NaLuF4 glass-ceramics (GCs) doped with Tm3+ and Tm3+/Yb3+ have been prepared by melting-quenching followed by thermal treatment at temperatures near the glass transition temperature. The crystallization process has been studied using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). NaLuF4 nanocrystals (NCs) ranging 9–30 nm in size are the only crystalline phase, the crystal size increasing with the dopant concentration. Energy dispersive X-ray (EDX) measurements confirm the Tm3+ and Yb3+ incorporation in the NCs. Optical characterization included the analysis of up-conversion (UC) as well as the Near-infrared (NIR) luminescence. NIR emission spectra of Tm3+ and Yb3+ in co-doped samples confirmed an efficient energy transfer between both ions. No UC emissions are observed in Tm3+ single-doped glass and GCs. Yb3+ incorporation favors the Tm3+-Tm3+ UC processes resulting in Tm3+ blue, yellowish-red and NIR UC emissions after excitation at 975 nm. Blue UC emission is also observed in the codoped samples after Tm3+ excitation at 791 nm. These effects were more evident for the GCs compared to the base glasses, confirming the RE ions incorporation in the NCs. As a result, these GCs can be used to tune the UC emission from NIR to blue by selective excitation., This work was supported by MINECO under Projects MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE), Basque Country Government PIBA2018-24 and Basque Country University GIU17/014. This article is part of the dissemination activities of project FunGlass. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 739566. This article was also created in the frame of the project Centre for Functional and Surface Functionalized Glass (CEGLASS), ITMS code is 313011R453, operational program Research and innovation, co-funded from European Regional Development Fund. This research work has been supported by the Research Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic, by the project: Advancement and support of R&D for "Centre for diagnostics and quality testing of materials" in the domains of the RIS3 SK specialization, Acronym: CEDITEK II., ITMS2014+ code 313011W442.

Transparent oxyfluoride glass-ceramics (GCs) with embedded β-Na1.5Y1.5F6 crystals doped with Er3+ ions were fabricated by a melt-quenching method with subsequent heat-treatment. The structural characterizations and spectroscopic techniques were performed to verify the precipitation of β-Na1.5Y1.5F6 crystals and partition of the Er3+ dopant into the crystals. Bright green up-conversion (UC) emission was achieved in Er3+-doped glass-ceramic (Er-GC). Furthermore, the temperature-dependent visible UC behavior based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) was also examined in the temperature range 298 k to 823 K with maximum relative sensitivity (Sr) of 1.1% K−1 at 298 K for TCLs in Er-G and Er-GC samples.

Transparent oxyfluoride glass&ndash, ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0 mol%&ndash, 2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9&ndash, 30 nm were obtained after heat treatments at Tg + 20&ndash, 80 &deg, C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass&ndash, ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.

The crystallization mechanism of LaF3 in sol-gel oxyfluoride glass-ceramics in the system SiO2-LaF3 has been studied using DTA, XRD, FTIR, HRTEM and NMR. Based on classical calculations of non-isothermal DTA curves involving Ozawas's plots, a diffusion-controlled process should be responsible for the fluorides crystallization similarly to that obtained for melt-quenching oxyfluoride glass-ceramics. Therefore, an increase of the crystal size and fraction is expected when increasing the time and/or temperature of the treatment. Nevertheless, XRD, FIR, HRTEM and NMR demonstrated that neither bigger crystals nor higher crystal fraction are obtained for treatment times longer than 1 min at 550 °C. However, further heat treatment causes that the structural order of the crystals is lost. On the other hand, typical fluorides crystallization temperatures (~300 °C) in sol-gel materials are much lower than Tg of the matrix (~1130 °C) thus being very different to what observed for oxyfluoride glasses prepared by melt-quenching. The proposed crystallization mechanism is a fast process that occurs when crystallization temperature is reached. This behavior is explained as a chemical reaction from the xerogels, followed by the fast precipitation of the nanocrystals without energy barrier. The nanocrystals are unstable in the surrounding SiO2 matrix for aging at crystallization or higher temperatures. These treatments lead to a dissolution process, favored by the compositional gradient between matrix and crystals, which drive the material to reach the equilibrium.

Transparent oxyfluoride glass-ceramics (GCs) were prepared starting from the glass composition 70SiO2–7Al2O3–16K2O–7LaF3 (mol%) doped with four different Nd3+ concentrations (0.1–2 mol%). The glass-ceramics were prepared by heat treatment above the corresponding glass transition temperatures (Tg + 10–100 °C). Depending on the Nd3+ concentration, cubic (α-phase) and hexagonal (β-phase) KLaF4 nanocrystals (NCs) precipitated from the starting glass. By X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM), the crystallization of the cubic structure was observed for all compositions, while β-KLaF4 nanocrystals were mostly detected for the glass-ceramic samples doped with 0.5 mol% NdF3. This noteworthy result is confirmed by site-selective laser spectroscopy. The presence of α-KLaF4 and β-KLaF4 crystalline phases is unambiguously identified from the emission and excitation spectra and lifetime measurements of the 4F3/2 state of Nd3+ ions. The spectroscopic results confirm those obtained with XRD and HR-TEM techniques: α-KLaF4 NCs are found to be present for all NdF3 concentrations whereas β-KLaF4 NCs are predominant in the glass-ceramic samples doped with 0.5 mol%., This work was supported by MINECO under projects MAT2013-48246-C2-1-P/-2-P and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country University PPG17/07 and GIU17/014. We acknowledge the European Syncrothron Radiation Facility for the provision of synchrotron radiation facilities in using the beamline BM25-SpLine to perform the experiments MA-3350 and 25-01-1014. Aluisio A. Cabral and Jose Joaquín Velázquez also acknowledge CAPES (#BEX 2598/15-9) and MINECO for Grant FPDI-2013-16895, respectively.

TiO2 nano-particles based photocatalysts were modified with different Pt percentages photodeposited on the surface, optimizing the method in order to obtain the best performance for the production of hydrogen. For testing hydrogen production, a novel reaction setup equipped with an elliptical cylindrical reflector to focus the radiation on the reactor has been used, being possible to control the reaction temperature. The hydrogen production has been measured in continuous by means of mass spectrometry. The effects of the reaction temperature and of the sacrificial reagent (methanol, ethanol or isopropanol) on the photocatalytic activity of Pt-TiO2 were studied. The best results at 25 °C were achieved for 2 wt% Pt-TiO2 (2Pt-TiO2) using methanol as sacrificial reagent, with a large maximum production over 16.0 mmol g−1h−1, which decreases to the half of this value after a long period of 72 h. These H2 production rates are larger, by a factor close to 30, than the ones obtained for the commercial P25 TiO2 in the same experimental conditions. The effect of the reaction temperature was analyzed on 2Pt-TiO2/water and 2Pt-TiO2/water/MeOH systems in the temperature range 5–60 °C. The apparent activation energy was determined for both photocatalysts, obtaining values of 17.5 and 23.3 kJ mol−1, respectively. The hydrogen production increases continuously with temperature in this range, achieving at 60 °C a H2 production of 0.83 and 38.0 mmol g−1h−1 for the photocatalyst in water and water/MeOH, respectively, after 2 h of reaction time.

Transparent oxyfluoride nano-glass-ceramics have been prepared by melting-quenching and doped with five different Nd3+ concentrations (0.1–2 mol%) to obtain the most efficient 4F3/2 → 4I11/2,13/2 emission. It was observed by differential thermal analysis (DTA) that the addition of Nd3+ does not affect the crystallization mechanism which corresponds to a diffusion-controlled volumetric process that starts from a constant number of nuclei. Nevertheless, the presence of the dopant affects the kinetics due to the progressive increase of Tg on increasing the Nd3+ content. LaF3 crystals with a size between 9 and 12 nm are obtained after heat treatments at Tg + 20–80 °C as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis shows the incorporation of Nd3+ ions into the LaF3 nano-crystals. Judd-Ofelt analysis from the absorption spectra further demonstrate the incorporation of Nd3+ ions into the fluoride phase and the most relevant parameters such as radiative lifetime and stimulated emission cross-section are calculated. A detailed optical characterisation clearly shows that Nd3+ ions in the glass-ceramics are incorporated in both crystalline and amorphous phases. Low temperature site-selective emission and excitation spectra, together with the different lifetime values of the 4F3/2 state depending on the excitation and emission wavelengths, allow emission from Nd3+ ions in the LaF3 nanocrystals to be identified and correlated with the structural properties. As the Nd3+ concentration is increased beyond 0.1 mol%, a stronger quenching of lifetime is observed for Nd3+ ions residing in LaF3 crystals than for those dispersed in the glass matrix. This strong concentration quenching is explained by the much higher concentration of Nd3+ ions in the crystalline phase with respect to that in the glass matrix.

Novel transparent oxyfluoride nano-glass-ceramics containing undoped and 0.5 Eu (mol%) doped NaGdF nanocrystals (NCs), were obtained by sol-gel for the first time. X-ray diffraction (XRD) confirms the precipitation of α- and β-NaGdF NCs with a size ranging between 5 and 24 nm. When the Na:Gd ratio, temperature and heating time are fixed to 0.95:1, 550–600 °C and 1–8 h, respectively, only the β-NaGdF phase precipitates. These results are confirmed by high-resolution transmission electron microscopy (HRTEM). The decomposition of trifluoroacetic acid (TFA) and the formation of fluoride lattice bonds were studied by Fourier transform infrared spectroscopy (FTIR). Thus, the sol-gel route permits NaGdF glass-ceramics to be obtained through the control of Na:Gd ratio, temperature and heating time. The incorporation of dopant ions in the NaGdF NCs was confirmed by photoluminescence measurements which show narrow and well-resolved Eu emission and excitation spectra in GCs. Moreover, the low asymmetry ratio values between the electric dipole (D → F) to the magnetic dipole (D → F) transitions indicate that Eu ions are incorporated in the NaGdF NCs. Furthermore, efficient Gd→ Eu energy transfer results in an enhancement of the reddish Eu emissions, further supported by fluorescence decay lifetimes., This work was supported by MINECO under Projects N° MAT2013-48246-C2-1-P/2-P and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE),and Basque Country University PPG17/07 and GIU17/014. This paperis a part of dissemination activities of the project FunGlass. This projecthas received funding from the European Union's Horizon 2020 researchand innovation programme under grant agreement No 739566

Novel glass-ceramic optical fibers containing NaLuF

Transparent oxyfluoride glass-ceramic films and self-supported layers with composition 80SiO2-20LaF3 doped with Er3+ have been successfully synthesized by sol-gel process for the first time. Crack-free films and self-supported layer with a maximum thickness up to 1.4 µm were obtained after heat treatment at the low temperature of 550 °C for 1 min, resulting in a LaF3 crystal fraction of 18 wt%, as confirmed by quantitative Rietveld refinement. This is the highest value reported up to now for transparent oxyfluoride glass-ceramics prepared by sol-gel. This work provides a new synthesis strategy and opens the way to a wide range of potential applications of oxyfluoride glass-ceramics. The characterization by a wide range of techniques revealed the homogeneous precipitation of LaF3 nanocrystals into the glass matrix. X-ray absorption spectroscopy and electron paramagnetic resonance confirmed that the Er3+ ions are preferentially embedded in the low phonon-energy LaF3 nanocrystals. Moreover, photoluminescence (PL) measurements confirmed the incorporation of dopants in the LaF3 nanocrystals. The effective concentration of rare-earth ions in the LaF3 nanocrystals is also estimated by X-ray absorption spectroscopy., This research was funded by Spanish National projects MAT2017-87035-C2-1-P/2-P (AEI/FEDER, UE), MAT2016-75362-C3-1-R, and Basque Country University PPG17/07 and GIU17/014, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Trabajo presentado en SPIE OPTO, celebrado en San Francisco (Estados Unidos), del 2 al 7 de febrero 2019, Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition 70SiO2–7Al2O3–16K2O–7LaF3 (mol%) are investigated. Site-selective laser spectroscopy demonstrates that depending on the Nd3+ concentration, cubic (α-phase) and hexagonal (β-phase) KLaF4 nanocrystals precipitate from the starting glass. The presence of both crystalline phases are unambiguously identified from the emission and excitation spectra and lifetime measurements of the 4F3/2 state of Nd3+ ions. The spectroscopic results are in agreement with those obtained with XRD and HR-TEM techniques: α-KLaF4 nanocrystals are found to be present for all NdF3 concentrations whereas β-KLaF4 nanocrystals are predominant in the GC samples doped with 0.5 mol%.

Transparent oxyfluoride nano-glass-ceramics (GCs) containing GdF3 nanocrystals undoped and doped with 0.5 Eu3+ (mol%) were obtained by a novel sol–gel method after sintering at temperatures such low as 550 °C. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show the precipitation of GdF3 nanocrystals with size between 7 and 10 nm, depending on the crystalline phase (hexagonal or orthorhombic) and the heating time. Fourier transform infrared spectroscopy (FTIR) analysis allows following the system evolution during the heat treatment showing the decomposition of trifluoroacetic acid (TFA), used as fluorine precursor, together with the formation of fluoride lattice bonding. Energy dispersive X-ray (EDX) analysis confirms the incorporation of the RE ions in the fluoride nanocrystals in the GCs. The ions incorporation on the GdF3 crystals is also supported by optical characterisation. Photoluminescence measurements result in a well resolved structure together with a narrowing of the Eu3+ emission and excitation spectra in the GCs compared to the xerogel. Moreover, the asymmetry ratio between the electric dipole transition (5D0→7F2) to the magnetic dipole transition (5D0→7F1) is reduced in GCs, indicating that Eu3+ ions are incorporated in the GdF3 crystalline phases. Moreover, Gd3+→Eu3+ energy transfer with enhancement of the energy transfer efficiency was observed in the GCs, further supported by fluorescence decay curves., This work was supported by MINECO under Projects N° MAT2013-48246-C2-1-P, MAT2013-48246-C2-2-P and Basque Country University PPG17/07 and GIU17/014. The authors thank the access to the Spanish Beamline (SpLine) at the ESRF facilities in Grenoble. J.J. Velázquez also acknowledges MINECO under Grant FPDI-2013-16895. This paper is also a part of dissemination activities of project FunGlass. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 739566.

[EN] Novel glass-ceramic optical fibers containing NaLuF nanocrystals doped with 0.5ErF and 2YbF (mol%) have been prepared by the rod-in-tube method and controlled crystallization. NaLuF nanocrystals with a size around 20 nm are obtained after heat treatment at 600 °C. Intense upconverted green and red emissions due to (H, S) → I and F → I transitions, respectively, together with a blue emission due to H → I transition have been observed under excitation at 980 nm. The intensity of the green and red upconversion bands shows a nearly linear dependence on the excitation power which can be explained by saturation effects in the intermediate energy states and proves that a sensitized energy transfer upconversion process is responsible for the population of the emitting levels of Er ions. The upconversion emission color changes from yellow to green by increasing the excitation power density which allows to manipulate the color output of the Er emission in the glass-ceramic fibers. The tunable emission color is easily detected with the naked eye. This interesting characteristic makes these glass-ceramic fibers promising materials for photonic applications., This work was supported by MINECO under the project MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country University PPG17/07 and GIU17/014, and Basque Government PIBA2018-24. Funding from MPNS Cost Action MP1401 is also acknowledged. This paper is a part of dissemination activities of project FunGlass. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 739566.

We present research on Ca3Sc2Si3O12 garnets doped with Ce3+ and Er3+ ions that were synthesized by the freeze-drying precursor method. The structural characterization was performed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) images of the calcined material were studied. Nanocrystals of Ca3Sc2Si3O12 were obtained by calcining the precursor at 1200 degrees C for 4 h with a mean size of about 100 nm. The luminescence features of Ce3+ and Er3+ doped samples indicated that these ions are effectively incorporated into the crystalline phase. In addition, codoping with Ce3+-Er3+ ions results in energy transfer processes from Ce3+ to Er3+ ions which led to the enhancement of near-infrared luminescence at 1.5 mu m. The efficiency of this non-radiative energy transfer process has been studied by means of excited state dynamics as a function of the doping concentration. From these results we have found that near-infrared Er3+ luminescence efficiency under VIS Ce3+ excitation is at maximal for 1Ce(3+)-1Er(3+) codoped Ca3Sc2Si3O12 garnets (in mol%). Luminescence quenching at higher Er3+ ion concentrations is observed.

This article belongs to the Special Issue Sol-Gel Chemistry Applied to Materials Science., Transparent glass-ceramics have shown interesting optical properties for several photonic applications. In particular, compositions based on oxide glass matrices with fluoride crystals embedded inside, known as oxyfluoride glass-ceramics, have gained increasing interest in the last few decades. Melt-quenching is still the most used method to prepare these materials but sol-gel has been indicated as a suitable alternative. Many papers have been published since the end of the 1990s, when these materials were prepared by sol-gel for the first time, thus a review of the achievements obtained so far is necessary. In the first part of this paper, a review of transparent sol-gel glass-ceramics is made focusing mainly on oxyfluoride compositions. Many interesting optical results have been obtained but very little innovation of synthesis and processing is found with respect to pioneering papers published 20 years ago. In the second part we describe the improvements in synthesis and processing obtained by the authors during the last five years. The main achievements are the preparation of oxyfluoride glass-ceramics with a much higher fluoride crystal fraction, at least double that reported up to now, and the first synthesis of NaGdF₄ glass-ceramics. Moreover, a new SiO₂ precursor was introduced in the synthesis, allowing for a reduction in the treatment temperature and favoring hydroxyl group removal. Interesting optical properties demonstrated the incorporation of dopant ions in the fluoride crystals, thus obtaining crystal-like spectra along with higher efficiencies with respect to xerogels, and hence demonstrating that these materials are a suitable alternative for photonic applications., This work was supported by MINECO under projects MAT2013-48246-C2-1-P, MAT2013-48246-C2-2-P, and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country Government IT-943-16 and PPG17/07. The authors are grateful for access to the Spanish Beamline (SpLine) at the ESRF facilities in Grenoble to perform experiments MA-3350 and 25-01-1014. Jose Joaquín Velázquez also acknowledges MINECO for Grant FPDI-2013-16895.

Transparent oxyfluoride nano-glass-ceramics (GCs) containing NaGdF4 nanocrystals doped with 0.1Pr3+and 0.5Pr3+, and co-doped with 0.5Pr3+-2Yb3+ ions (mol%) were obtained by melting-quenching followed by heat treatments at temperatures near Tg. The addition of rare-earths (RE) ions affects the crystallization kinetics due to the progressive increase of Tg as RE concentration increases. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show the precipitation of NaGdF4 nanocrystals with sizes between 9 and 30 nm. The crystal size increases with the increasing amount of dopant. Energy dispersive X-ray (EDX) analysis confirms the incorporation of the RE ions in the fluoride nanocrystals in the glass-ceramics. This incorporation is also supported by optical characterization. Photoluminescence measurements shows a better resolved structure together with a narrowing of the Pr3+ emission and excitation spectra in the glass–ceramics compared to the precursor glass. The emission spectra and fluorescence decay curves from the 3P0 level of Pr3+ in the codoped samples support the existence of a Pr3+ → Yb3+ energy transfer with slight enhancement of the energy transfer efficiency in the GC sample., This work was supported by MINECO under Projects MAT2013-48246-C2-1-P and MAT2013-48246-C2-2-P and Basque Country UniversityPPG17/07. J.J. Velázquez also acknowledges MINECO under Grant FPDI-2013-16895. Gang Chen acknowledges the U.S. National Science Foundation for partial support under Grant #DMR-1507670.

Trabajo presentado al SPIE Photonic West: Optical Components and Materials XV, celebrado en San Francisco, California (USA) del 29 al 31 de enero de 2018., Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition SiO2-Al2O3-Na2O-LaF3 are investigated. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) show that the precipitated nanocrystals are LaF3 with a crystal size between 9-12 nm. Furthermore, energy dispersive X-ray (EDX) analysis shows the incorporation of Nd3+ ions into the LaF3 nanocrystals. Site-selective and time-resolved emission and excitation spectra of the 4F3/2 and 4F5/2 states, allows to unambiguously isolate the emission of Nd3+ ions in LaF3 nanocrystals which shows well defined spectra, similar to those obtained for pure LaF3 crystal., This work was supported by the Spanish Government MEC under Projects No. MAT2013-48246-C2-1-P, MAT2013-48246-C2-2-P, and MAT2017-87035-C2-2-P and the University of the Basque Country PPG17/07.

Nanostructured glass-ceramics obtained by the adequate heat treatment of a Nd3+-doped glass with composition SiO2-Al2O3-Na2O-LaF3 have been investigated by several techniques. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) show that the precipitated nanocrystals are LaF3 with a crystal size between 9 and 13 nm. Furthermore, energy dispersive X-ray (EDX) analysis shows the incorporation of Nd3+ ions into the LaF3 nano-crystals. A detailed optical characterization clearly shows that Nd3+ ions in glass-ceramics are incorporated in both crystalline and amorphous phases. Steady-state and time-resolved site-selective laser spectroscopies allow to isolate unambiguously the emission of Nd3+ ions in LaF3 nanocrystals which shows extremely well defined spectra, similar to those obtained for pure LaF3 crystal.

Transparent glass ceramic (GC) films and self-supported layers of composition 80SiO-20LaF doped with Nd were prepared by sol-gel method for the first time. GC films were deposited by dip coating on different substrates and heat-treated between 350°C and 850°C for 1, 3, and 80 hours. The structural analysis of thin films was performed by GI-XRD and HR-TEM to check the LaF nanocrystals precipitation in the SiO matrix, revealing a crystal size lower than 5 nm. The emission and excitation spectra and lifetimes of the films have been obtained for different thermal treatments and Nd contents. The luminescence intensity of the F →I laser transition increases with the treatment temperature and Nd content, whereas a reduction for the luminescence lifetime is observed compared to those observed in bulk samples prepared by melting quenching., This work was supported by MINECO sunder Projects No. MAT2013‐48246‐C2‐1‐P and MAT2013‐48246‐C2‐2‐P and Basque Country University PPG17/07. J.J. Velázquez also acknowledges MINECO under Grant FPDI‐2013‐16895.

Resumen del trabajo presentado a la Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference, celebrada en Munich (Alemania) del 25 al 29 de junio de 2017., The growing field of photonics demands the design of new rare-earth (RE)-based optical materials for their use in optical telecommunications, solid state lasers, three-dimensional full-color displays, solar cells, and others. Oxyfluoride glass-ceramics are promising RE hosting candidates since they combine the good chemical and mechanical stability of oxide glass matrixes with the good optical properties of low phonon energy fluoride nano-crystals. In this work, transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition SiO2-Al2O3-Na2O-LaF3 are investigated. This glass-ceramic contains very small LaF3 crystals (a10 nm), being LaF3 among the best fluoride hosts for RE ions. Site-selective and time-resolved emissions and excitation spectra of the 4F3/2 and 4F5/2 states, allows to unambiguously isolate the emission of Nd3+ ions in LaF3 nanocrystals which shows extremely well defined spectra, similar to those obtained for pure LaF3 crysta. As an example Fig.1(a) shows the low temperature emission spectra obtained by exciting at 786 and 802 nm for the glass-ceramic sample doped with 0.1 mol% of Nd3+ treated at 620 oC-40h. The spectrum obtained under excitation at 786.5 nm shows sharp peaks. The one at 1039 nm does not overlap with the emission spectrum obtained by exciting at 802 nm. The sharp peaks disappear and the spectrum becomes broader and similar to that found in the glass sample for 802 nm excitation. These results indicate that in the glassceramic samples excited at 786.5, Nd3+ ions are mainly in the crystalline phase. As concentration increases, the emission from Nd3+ ions in the NCs decreases, and the spectra become broader and with less resolved peaks. The excitation spectra also confirm the presence of Nd3+ in the NCs. The low temperature excitation spectra are presented in Fig.1(b) for the GC sample doped with 0.1 mol%. As observed in the spectra obtained at 1039 nm, the low energy band corresponding to the 4I9/2o4F3/2 doublet narrows and defines into two single components as expected for a well defined crystal field site. Moreover, the 4I9/2o4F5/2 band is composed of narrow and well resolved peaks which indicates that the spectra obtained at 1039 nm correspond to Nd3+ ions in the LaF3 nanocrystals. On the other side, the spectra obtained at 1055 nm shows broad bands similar to those found in the glass samples. As concentration increases, the emission from Nd3+ ions in the NCs decreases, and the spectra become broader and with less resolved peaks.

Visible-to-UV/violet upconversion luminescence is found and studied in oxyfl uoride glass ceramics with Er 3+ dopant concentrations of 3.5, 6.0, or 12.0 mol%, covering a broad pump-power range. The glass ceramics with doping levels of 3.5 and 6.0 mol% show the strongest upconversion luminescence intensity when compared to both higher doping levels and the respective precursor glasses. A comprehensive analysis of the involved upconversion mechanisms is presented. These materials could be useful to enhance the effi ciency of the water-splitting systems by using UV/violet light upconverted from the green and red parts of the solar spectrum, which are an alternative to photovoltaic solar cells.

Transparent oxyfluoride glass-ceramic fibers containing LaF nanocrystals have been drawn using a single crucible method and crystallization after an appropriate heat treatment. Optical fibers have been obtained a posteriori through the deposition of SiO cladding prepared by sol-gel and deposited by dip-coating. Detailed thermal and structural characterization performed by DTA, XRD, HRTEM and SAXS showed the good reproducibility of the technology. Phase separation, due to fluorine immiscibility in an oxide glass matrix, initiates the crystallization. The crystallization mechanism is a diffusion-controlled process and the local compositional changes of the glass matrix around the nanocrystals limit the crystal size to 10-20 nm depending on the treatment conditions. The optical characterization demonstrated the light propagation into the glass-ceramic core and the possibility to selectively excite Nd ions in the fluoride nanocrystals with a corresponding increase of the luminescence efficiency., This work was supported by MINECO under Project No. MAT2013-48246-C2-1-P and MAT2013-48246-C2-2-P and Basque Country University PPG17/07. J. J. Velázquez also acknowledges MINECO under Grant FPDI-2013-16895. G. Chen acknowledges the U.S. National Science Foundation for partial support under Grant #DMR-1507670.

Lithium luminescent ZnO:Li nanocrystals have been synthesized. Atomic absorption and optical spectroscopy confirm the high doping level of Li up to 5 at% can be achieved and indicate that the dopants may form neutral Li–Li dimers. The 100 nm width and several milliseconds lifetime long luminescence of the proposed Li–Li dimers occurs around 770 nm and is excited by energy transfer from the ZnO host when pumped in the range between 250 and 420 nm. These parameters of Li-related luminescence have been explained in terms of the energy level diagram of Li–Li dimers, where the Li luminescence is excited by spin-allowed singlet–singlet transitions and occurs due to spin-forbidden triplet–singlet transitions of Li–Li dimers. The milliseconds lifetime of the emitting level of Li dimers and nanosecond lifetime of the feeding state of the ZnO point out a 3-level lasing system. This Li luminescence may be used for the broad spectral range down-conversion of solar spectrum for enhanced efficiency solar cells. The sites for the Li–Li dimers have been proposed, where Li atoms locate in octahedral voids of Zn and O sub-lattices.

95SiO 2 –5LaF 3 sol–gel derived nano-glass–ceramics single doped with Ce 3+ or Tb 3+ and co-doped with Ce 3+ –Tb 3+ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF 3 nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb 3+ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce 3+ to Tb 3+ ions in the glass–ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF 3 nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.

95SiO2–5LaF3 sol-gel derived nano-glass-ceramics single doped with Eu3+ or Sm3+ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF3 nanocrystals after the ceramming process, with mean size ranging from 10 to 20 nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF3 nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu3+ and Sm3+ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions.

In this work the use of HF/HNO3 solutions for texturing silicon-based solar cell substrates by stain etching and the influence of texturing on minority carrier lifetimes are studied. Stain etching is currently used to decrease the reflectance and, subsequently improve the photogenerated current of the cells, but also produces nanostructures on the silicon surface. In the textured samples it has been observed that an improvement on the minority carrier lifetime with respect to the samples treated with a conventional saw damage etching process is produced on grain boundaries and defects, and the origin of this effect has been discussed.

Sol–gel derived glass–ceramics containing CeF3 nanocrystals have been developed for the first time, to the best of our knowledge, by adequate heat treatments of precursor bulk glasses with composition 95SiO2–5CeF3 doped with 0.1 Eu3+ or 0.1 Sm3+ and co-doped with 0.3 Yb3+ and 0.1 Er3+ ions (in mol%). X-Ray Diffraction and High Resolution Transmission Electron Microscopy confirm the precipitation of CeF3 nanocrystals. Moreover, this structural analysis is completed using Eu3+ and Sm3+ as probe ions of the different local environments for rare-earth ions in the nano-structured glass–ceramics. Luminescence measurements led us to discern the final environments for the ions, revealing the partition of a large fraction of these ions into like-crystalline environment of the precipitated CeF3 nanocrystals. Near infrared emission at 1.5 μm was observed after excitation at 980 nm in Yb3+–Er3+ co-doped samples for potential applications in telecommunications.

In this work, erbium and ytterbium have been incorporated into luminescent porous silicon (PS) layers by simple impregnation of the PS substrate with a saturated nitrate solution of erbium and ytterbium. The photoluminescence of the co-doped rare earth layers have been evaluated. The doping process has been designed for its potential in silicon-based solar cell production, with the aim to improve the Shockley–Queisser limit with a reasonable cost effective method for the industry, which implies a significant enhancement of the efficiency under non-concentrated sunlight irradiation. The temperature and annealing time of the doping process were selected according to industry standards in order to ease a trial adoption. The composition was analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy in order to characterize the doping profile. Different up-conversion and down-conversion contributions from the rare earths in the visible and IR were detected, together with the down shifting effect of the stain etched PS. There is no evidence of energy transference between the PS matrix and the rare earths.

Sol-gel glasses with composition (100−x)SiO2–xSnO2 doped with 0.4 mol% of Sm3+, with x ranging from 1 to 10, have been successfully synthesized. Transparent doped nano-glass-ceramics were prepared by thermal treatment of the precursor glasses at 900°C during 4 hours, leading to nanocomposites comprising SnO2 nanocrystals embedded into an amorphous SiO2 phase. A structural analysis in terms of X-ray Diffraction and High Resolution Transmission Electron Microscopy confirms the precipitation of SnO2 nanocrystals within the glassy matrix. The mean radius of the obtained SnO2 nanocrystals, ranging from 2.1 to 4.7 nm calculated by the Scherrer and Brus equations, similar to the Bohr’s exciton radius, constitutes a wide band-gap semiconductor quantum-dot system. Energy transfer from SnO2 nanocrystal host to Sm3+ ions is confirmed by luminescence spectra and analyzed as a function of SnO2 concentration, showing an evolution that could be ascribed to selective excitation of nanocrystal sets with predetermined size. Besides, a study of the luminescence as a function of temperature helps to clarify the involved energy transfer mechanisms.

The up-conversion of near infrared photons into the visible range is of major interest for lighting appliances and photonic integrated devices. Here we report up-conversion luminescence in transparent nano-glass-ceramics with composition of 95SiO2–5LaF3 co-doped with 0.1 mol% of Pr3+ and 0.3 mol% of Yb3+, which were synthesized by different thermal treatments of precursor sol–gel glasses. Precipitation of LaF3 nanocrystals during ceramming process was confirmed by means of X-ray diffraction and the partition of rare-earth ions into them has been analyzed. The effect of increasing thermal treatment temperature and adding Yb3+ ions in the degree of crystallinity of the samples has been discussed. Efficient up-conversion emissions were observed under infrared excitation of the Yb3+ ions in the co-doped Yb3+–Pr3+ samples, while it was hardly detected in single Pr3+-doped samples.

Transparent nano-glass–ceramics of composition 95SiO 2 –5SnO 2 mol%, single doped with 0.4 mol% of Tb 3+ and co-doped with 0.4 mol% of Eu 3+ and Tb 3+ have been obtained by thermal treatment of precursor sol–gel glasses. The segregated SnO 2 nanocrystals, precipitated in the insulator SiO 2 glass matrix during heat treatment, constitute a wide band gap quantum-dot system with mean radius of nanocrystals around 2.2–2.8 nm, comparable to the bulk exciton Bohr radius. A fraction of the rare earth ions is incorporated to the SnO 2 nanocrystals and can be excited by energy transfer from the semiconductor host. The efficiency of this energy transfer process is strongly dependent on the nanocrystal radius in the case of the Tb 3+ ions, whereas the dependence is not appreciable in the case of Eu 3+ ions. These results can be explained taking into account the variations of the overlap of the SnO 2 broad visible emission due to oxygen vacancies with the rare earth excitation spectra.

Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 co-doped with 0.3Yb3+, 0.1Ho3+ and 0.1Tm3+ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron microscopy analysis point out the precipitation of hexagonal LaF3 nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power.

The room temperature near-infrared emission at 1.06 μm corresponding to the 4 F 3/2 → 4 I 11/2 laser transition in Nd 3+ -doped SiO 2 –LaF 3 transparent glass–ceramics prepared by sol–gel method has been characterized in terms of the product of emission cross-section and fluorescence lifetime. Stimulated emission cross-sections have been calculated from experimental emission spectra using the Fuchtbauer–Ladenburg equation. The precipitation of LaF 3 nanocrystals after heat-treatment, confirmed by X-ray diffraction, induces a significant increment of the 1.06 μm near-infrared emission compared with the as made sample. An enhancement of emission cross-section of about 10% has been achieved with increasing temperature of heat-treatment of the nano-ceramming process from 800 to 1000 °C, which is related to the growth of LaF 3 nanocrystals.

Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 doped with 0.1 mol% of Tm3+ or co-doped with 0.1 mol% of Tm3+ and 0.3 mol% of Yb3+ were synthesized by thermal treatment of precursor sol–gel derived glasses. A comparative luminescence analysis in terms of different temperatures of thermal treatments has been carried out. Segregation of LaF3 nanocrystals in the matrix was con- firmed by X-ray diffraction. Blue and red efficient up-conversion emissions were observed under 980 nm excitation at room temperature. These results indicate partition of a significant fraction of co-dopants into the precipitated LaF3 nanocrystals. The mechanisms involved in the up-conversion emissions have been analyzed and can be ascribed to processes with two, three and four photons. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Transparent glass-ceramics with composition of 95SiO 2 -5LaF 3 doped with 0.1 mol% of Ho 3+ or co-doped with 0.1 mol% of Ho 3+ and 0.3 mol% of Yb 3+ were synthesized by thermal treatment of precursor sol-gel glasses. Segregation of LaF 3 nanocrystals in the matrix was confirmed from a structural analysis by means of X-ray diffraction. Blue, green and red efficient up-conversion emissions were observed under 980 nm excitation at room temperature. These results could be attributed to the partition of a fraction of Ho 3+ ions into the precipitated LaF 3 nanocrystals. Moreover, near infrared down-conversion at 1.2 μm is also observed. The mechanisms involved in the up-conversion emissions could be ascribed to a two- and three-photon process.

Hysteresis loops of two-dimensional arrays of magnetic nanowires have been micromagnetically modelled. The calculations focus on magnetostatic interactions in addition to Zeeman and magnetic anisotropy energy terms. Starting from an ideally ordered hexagonal array, the generation of local disorder is first modelled and subsequently, hysteresis loops are calculated by Monte Carlo and iterative methods considering dipolar and higher-order multipole effects. The main conclusions of the modelling are: (i) distortion of the hexagonal ordering results in an increasing effective field to reach magnetic saturation while roughly maintaining coercivity, and (ii) an increase of the average distributed coercivity of individual nanowires gives rise to enhanced coercivity and anisotropy field. The results of these simulations are analysed in view of experimental loops of arrays of Ni nanowires filling nanoporous alumina membranes with different degrees of 2D-polycrystalline arrangement. After a careful analysis by image processing, it is concluded that fluctuations in the diameter and cross-section of individual nanowires play an important role in a deep correlation between modelled and experimental hysteresis loops.

Ca3Sc2Si3O12 garnets doped with Ce3+ and Tb3+ ions were synthesized by a freeze-drying precursor method. The structural characterization was performed by X-ray diffraction (XRD) and Raman spectroscopy. Scanning Electron Microscopy (SEM) images of the calcined material were studied. High temperature treatments and doping with RE3+ ions resulted in a reduction of the secondary phases (Sc2O3) and an increase of the mean size of the nanocrystals, from 75 to 149 nm. These effects were confirmed by means of Raman spectra. Moreover, luminescence features of Ce3+ and Tb3+ doped samples indicated that these ions are effectively incorporated into the crystalline phase. In addition, the energy transfer processes between Ce3+ and Tb3+ ions in codoped garnets have been studied. (C) 2015 Elsevier B.V. All rights reserved.

The unbalanced distribution of magnetic poles at the ends of the bistable Fe-based magnetostrictive glass-coated amorphous microwires generates a magnetic stray field that interacts with magnetisation in neighbouring microwires. A theoretical model is developed to analyse the magnetisation process of a two-dimensional array of quasi-identical microwires, taking into account the symmetry of the distribution (hexagonal, cubic, random), the number of microwires, and the distance between them. The conditions are analysed for arrays which behave as a complex system, specifically a system with self-organised criticality where both distributions of microwires with parallel and antiparallel magnetisation follow a fractal patron, and also conditions when individual magnetisation reversals in the array extend to the neighbours, as well as the possibility of application of this effect in magnetic recording devices.

Fe-based magnetostrictive amorphous wires are bistable exhibiting square-shaped longitudinal hysteresis loops. This is a consequence of their particular domain structure that allows them to be approached as magnetic dipoles. Arrays of such bistables wires are accordingly shown to be coupled by magnetostatic interactions. Furthermore, an analysis of these interactions allows us to conclude that depending on the relative strength of the magnetostatic and Zeeman interactions, ordered, complex or chaotic behaviours are found in the temporal variation of the array magnetisation.

Aim: To implement an accessible strategy for detection of the Mexican founder mutation NG_005905.2:g.118973_133629del, located in BRCA1, which deletes exons 9-12 (BRCA1 ex9-12del), as part of the health care setting of patients with hereditary breast and ovarian cancer (HBOC), from the National Cancer Institute (Mexico). Material and methods: We designed a polymerase chain reaction (PCR) based method, for the targeted detection of the deletion of exons 9 through 12, of the BRCA1 gene. The method was validated with previously verified results of the deletion by multiplex ligation-dependent probe amplification assay (MLPA), or deep sequencing of the region. Finally, the technique was used for the detection of BRCA1 ex9-12del mutation in a group of 302 HBOC patients, in whom the existence of BRCA1 and BRCA2 point mutations had been ruled by pyrosequencing. Results: The concordance of our method, with previously reported BRCA1 ex9-12del mutation results, was 100%. Also, we provided a profile of the clinical and familial characteristics of 302 Mexican patients with clinical suspicion of HBOC, in whom the detection of BRCA1 ex9-12del mutation was performed. In this way, 21 patients (6.95%) were identified as BRCA1 ex9-12del mutation carriers. Among whom, a higher proportion of triple negative breast cancer was found (73% versus 21%, p=0.0005; two sided Fisher's exact test) . Conclusions: A feasible molecular diagnostic strategy for the detection of BRCA1 ex9-12del mutation was established in Mexican patients, with HBOC. In this way, we identified 21 (21/302) carriers of the deletion, who represented the 6.95%. Related to the clinical features, triple negative breast cancer carriers stood out. It had been reported that large genomic rearrangements in BRCA1 are associated with an increased frequency of high risk features. These type of approach is appropriate in populations where a founder effect is recognized. For its simplicity and effectiveness, it can be transferred to other laboratories, for the benefit of a greater number of Mexican patients and with the aim of minimize costs of testing. Because of the frequency of BRCA1 ex9-12del mutation, this method has been implemented as the first line of BRCA1 clinical genetic analysis in patients with suspected HBOC, at National Cancer Institute (Mexico ). Citation Format: Rosa M. Alvarez, Jose Velazquez, Veronica Fragoso, Julieta Dominguez, Paulina Nuñez, Talia Wegman, Yuliana Sanchez, Silvia Vidal, Enrique Bargallo, Dolores Gallardo, Abelardo Meneses, Luis A. Herrera. Screening for BRCA1 founder mutation in Mexican population: an accessible approach [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4278. doi:10.1158/1538-7445.AM2017-4278

Magnetization reversal of high and positive magnetostriction amorphous wires gives rise to a square hysteresis loop owing to their particular domain structure. When two quasi-identical wires are placed close together, the lack of simultaneous magnetization reversal produces a temporal instability in the hysteresis loop as a consequence of the magnetostatic interaction between them. This instability, having chaotic properties, is controlled by the amplitude and frequency of the applied magnetic field and depends on the length of the wires and distance between them. A theoretical model, based on an iterative algorithm, has been developed in order to understand the properties of the whole magnetization. The instability seems to originate in an irreversible rearrangement of the closure domain structure at the ends of the wires after each magnetization reversal. The magnetization of the set of wires follows a potential law that can be explained in the framework of the self-organized criticality, a theory of th...

Glass-coated hard-magnetic Fe - Co - Cr microwires were prepared by Taylor's technique with subsequent annealing at different temperatures. The diameter of the metallic core is . The annealing temperature dependence of the coercive force is reported; the maximum coercivity is about 200 Oe after an annealing at for one hour. Such materials may be useful in locally magnetizing devices and magnetic force microscopy.

We have measured and fitted the kinetics of luminescence of Ag nanoclusters homogeneously dispersed within the bulk of an oxyfluoride glass, with various sample temperatures. The balance equations for the populations of the excited singlet and triplet states of the Ag nanoclusters are proposed and used in this fitting while taking into account inter-system crossing between the singlet and triplet states and their wavelength dependent spontaneous decay to the ground singlet state. The involved energy barriers and rate constants and spontaneous emission cross-sections for the excited singlet and triplet states are evaluated.

As-prepared and heat-treated oxyfluoride glasses, co-doped with Ag nanoclusters/nanoparticles, are prepared at 0.15 at. % Ag concentration. The as-prepared glass shows an absorption band in the UV/violet attributed to the presence of amorphous Ag nanoclusters with an average size of 1.1 nm. The luminescence spectra of the untreated glass can also be ascribed to these Ag nanoclusters. Upon heat-treatment, the clusters coalesce into Ag nanoparticles with an average size of 2.3 nm, and the glasses show an extra surface plasmon absorption band in the visible. These particles, however, cease to emit due to ascribing plasmonic properties of bulk silver.

A comparative study of the remagnetization process of highly-magnetostrictive as-cast Fe-rich amorphous wires having different diameters (from 165 to 10 μm) and lengths (between 10 cm and 2 mm) is here reported for the first time. Wires obtained by conventional in-rotating-water quenching (165 down to 70 μm diameter) and by a modified Taylor's technique (2.5 μm glass cover on 10 to 15 μm diameter magnetic core) are studied. Macroscopic and local hysteresis loops are measured by induction technique with the help of large and very tiny pick up coils respectively. From the latter, the magnetization profile of these magnetically bistable wires is determined. The critical length to observe a single and large Barkhausen jump when remagnetizing decreases with the diameter of the sample. In particular, for the wires covered by glass the critical length to observe spontaneous bistability is less than 2 mm. Values of those critical lengths are interpreted taking into account the compromise between magnetostatic and magnetoelastic energy terms.