Transparent Glass-Ceramics Produced by Sol-Gel: A Suitable Alternative for Photonic Materials

Abstract

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.

Sol-Gel Glass-Ceramic Materials Containing CaF2:Eu3+ Fluoride Nanocrystals for Reddish-Orange Photoluminescence Applications

“…As was presented in Figure 5, the emission spectrum of CaF 2 :Eu 3+ GCs also consisted of the characteristic bands of Eu 3+ ions corresponding to the intra-configurational 5 The photoluminescence decay curve of the 5 D0 state of Eu 3+ ions recorded for fabricated glassceramics was presented in the inset of Figure 5. The decay curve was well-fitted to double-exponential function and therefore, it was distinguished two different decay components: fast (τ1 = 1.63 ms) and slow (τ2 = 12.84 ms).…”

“…Transparent glass-ceramics (GCs) containing fluoride nanocrystals fabricated using high-temperature melt-quenching or low-temperature sol-gel method are suitable modern materials for lasers, optical waveguides, solid-state lighting and numerous photonic applications [1][2][3][4][5]. Depending on chemical composition and technological conditions, nano-or micro-crystals are usually well-formed during temperature-controlled crystallization of precursor glasses or xerogels.…”

Nano-Structured Optical Fibers Made of Glass-Ceramics, and Phase Separated and Metallic Particle-Containing Glasses

“…The nanostructure of the PCGs can be obtained using transmission electron microscopy (TEM) and its high-resolution analogue (HRTEM), as it is demonstrated in [105][106][107][108]. In particular, HRTEM can be used to reveal the lattice planes and the crystal-size distribution.…”

“…Since then, there has been much interest in developing novel transparent oxyfluoride glass-ceramics containing REE-doped fluoride crystals. Reviews on transparent oxyfluoride GCs in bulk form can be found in [163] and [108]. Some of the first transparent oxyfluoride GC fibers were with the composition of 48SiO 2 -11Al 2 O 3 -7Na 2 CO 3 -10CaO-10PbO-11PbF 2 -3ErF 3 and 48SiO 2 -11Al 2 O 3 -7Na 2 CO 3 -10CaO-10PbO-10PbF 2 -3YbF 3 -1ErF 3 [105].…”

Effect of dopant precursors on the optical properties of rare‐earths doped oxyfluoride glass‐ceramics

“…Another great advantage of GCs with respect to other kinds of materials is related with the availability of different processing methods: from classical melt‐quenching (MQ) to sol‐gel (SG), that allows the preparation of materials as bulk, films, powder or fibers. Most works published up to date about oxyfluoride GCs concern bulk materials prepared MQ doped with RE ions, however, a review paper about SG oxyfluoride GCs was also published recently . Recently, the preparation of optical fibers with GC core has emerged as interesting field and several works have been published since 2015.…”