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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. ; Peer Reviewed

This article belongs to the Special Issue Preparation and Application of Nanostructured Glass–Ceramics and Nanocomposites. ; Transparent oxyfluoride glass–ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0–2 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 9–30 nm were obtained after heat treatments at Tg + 20–80 °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–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. ; This research was funded by Spanish National projects MAT2017-87035-C2-1-P/2-P (AEI/FEDER, UE), Basque Country University PPG17/07 and GIU17/014 and Basque Government PIBA2018-24. This study is part of the dissemination activities of project FunGlass. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 739566. This study 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. ; Peer reviewed

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. ; Peer reviewed

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. ; Peer reviewed

[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.

This article belongs to the Special Issue Glass-Ceramics: Improving Glass Properties through Crystallization. ; In this study, transparent oxyfluoride glass-ceramics (GCs) with NaLaF4 nanocrystals (NCs) were prepared by the sol–gel method for the first time. Three different molar ratios of La(CH3COO)3/Na(CH3COO) were used to obtain the GCs, which were sintered at 450, 550 and 650 °C for 1 min. X-ray diffraction (XRD) was employed to follow the evolution of the xerogel during the heat treatments and to study crystal growth for the three temperatures. In all cases, the LaF3 crystalline phase was present, but crystallization of NaLaF4 was only promoted at 650 °C. Thermogravimetric and thermodifferential analysis (TGA-DTA) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the crystallization process. High-resolution transmission electron microscopy (HRTEM) was employed to confirm NaLaF4 crystallization and determine the size distribution. The incorporation of Nd3+ ion into NaLaF4 and LaF3 nanocrystals was confirmed by site-selective emission and excitation spectra. The Nd3+ emission intensities in both phases depend not only on the NaLaF4/LaF3 ratio but also on their emission efficiencies. ; The authors acknowledge financial support from MINECO under projects MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE), and Basque Government PIBA2018-24. This article is a part of the dissemination activities of the project FunGlass, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 739566. ; Peer reviewed