Crystallization of Sol-Gel Derived Glasses

A special issue of Crystals (ISSN 2073-4352).

Deadline for manuscript submissions: closed (31 August 2017)

Special Issue Editors

Departamento de Engenharia Química/CQE, Instituto Superior Técnico/UL, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Interests: sol-gel films; photonic materials; photonic crystals; rare-earth luminescence; solid state lighting; frequency conversion; glass structure; glass crystallization
Special Issues, Collections and Topics in MDPI journals
Departamento de Engenharia Química/CQE, Instituto Superior Técnico/UL, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Interests: glass ceramics; photonic materials; glass crystallization; frequency conversion; optical characterization; rare-earth luminescence

Special Issue Information

Dear Colleagues,

Although the crystallization of glass is often a phenomenon to be avoided if spontaneous, a glass may also be made to undergo controlled crystallization. Therefore, the crystallization phenomena and the associated mechanisms, often in the presence of a nucleating agent, assume a critical role. As opposed to the case of bulk melted glasses, there is a lack of detailed studies of the crystallization kinetics of gels, sol–gel derived glasses and glassy films, due in part to experimental difficulties with films which represent the vast majority of sol–gel derived glassy materials prepared, and for which traditional tools such as DTA and DSC are difficult to use. However, these topics are gaining increasing interest, for example in view of developments on transparent nano glass-ceramics, which successfully combine the mechano-chemical stability of an oxide glass matrix with the luminescence properties of lanthanide ions embedded in crystal phases of low phonon energies. Therefore, the crystallization of gels and sol–gel derived glasses is increasingly becoming an active area of research.

The Special Issue on “Crystallization of Sol–Gel Derived Glasses” is intended to provide an international forum for all aspects of sol–gel glass crystallization compared to melted glasses, outlining the experimental techniques which are used.

Prof. Dr. Rui M. Almeida
Prof. Dr. Luís F. Santos
Guest Editors

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Keywords

  • Sol–gel glasses
  • Glass crystallization
  • Crystallization mechanisms
  • Nanoglass-ceramics

Published Papers (2 papers)

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5075 KiB  
Article
Interface Crystallization of Ceria in Porous Silica Films for Solar Applications
by Gundula Helsch and Joachim Deubener
Crystals 2017, 7(3), 80; https://doi.org/10.3390/cryst7030080 - 08 Mar 2017
Cited by 1 | Viewed by 4192
Abstract
Antireflective (AR) coatings with photocatalytic activity for solar cover glasses are extensively investigated at present, mostly in multilayer systems including titania. In this study, bifunctional single coats from porous silica in combination with up to 33 mol % ceria were prepared by sol–gel [...] Read more.
Antireflective (AR) coatings with photocatalytic activity for solar cover glasses are extensively investigated at present, mostly in multilayer systems including titania. In this study, bifunctional single coats from porous silica in combination with up to 33 mol % ceria were prepared by sol–gel dip-coating on low-iron soda-lime float glass. After heat treatment for one hour at 350 °C, the coated glasses were characterized. Solar transmittance decreased with increasing ceria content, whereas photocatalytic activity increases. Crystallization of cubic ceria was detected by grazing incidence X-ray diffraction. Chemical depth profiling by secondary neutral mass spectrometry revealed the enrichment of cerium at the coating surface as well as at the interface to the glass substrate. Self-assembled ceria crystallization at the interfaces resulted in a three-layered mesostructure of the coating, which was verified by field-emission scanning electron spectroscopy. Cubic ceria crystals at the interface act as a barrier for the sodium diffusion from the substrate, which prevents the poisoning of the photocatalyst, while those crystals at the surface act as an electron donor for photooxidation processes, both enabling adequate photocatalytic activity. The triple-layer architecture with the sequence of high/low/high refractive index materials allows for optical interference sustaining the AR-function. Full article
(This article belongs to the Special Issue Crystallization of Sol-Gel Derived Glasses)
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1106 KiB  
Article
Sol–Gel-Derived Glass-Ceramic Photorefractive Films for Photonic Structures
by Anna Lukowiak, Lidia Zur, Thi Ngoc Lam Tran, Marcello Meneghetti, Simone Berneschi, Gualtiero Nunzi Conti, Stefano Pelli, Cosimo Trono, B.N. Shivakiran Bhaktha, Daniele Zonta, Stefano Taccheo, Giancarlo C. Righini and Maurizio Ferrari
Crystals 2017, 7(2), 61; https://doi.org/10.3390/cryst7020061 - 21 Feb 2017
Cited by 23 | Viewed by 5277
Abstract
Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol–gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. [...] Read more.
Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol–gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. Here, we briefly discuss the state of the technology and show that the choice of the sol–gel as a synthesis method brings the advantage of process versatility regarding materials composition and ease of implementation. In this context, we present tin-dioxide–silica (SnO2–SiO2) glass-ceramic waveguides activated by europium ions (Eu3+). The focus is on the photorefractive properties of this system because its photoluminescence properties have already been discussed in the papers presented in the bibliography. The main findings include the high photosensitivity of sol–gel 25SnO2:75SiO2 glass-ceramic waveguides; the ultraviolet (UV)-induced refractive index change (Δn ~ −1.6 × 10−3), the easy fabrication process, and the low propagation losses (0.5 ± 0.2 dB/cm), that make this glass-ceramic an interesting photonic material for smart optical applications. Full article
(This article belongs to the Special Issue Crystallization of Sol-Gel Derived Glasses)
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