Crystallization Process and Site-Selective Excitation of Nd3+ in LaF3/NaLaF4 Sol–Gel-Synthesized Transparent Glass-Ceramics

Abstract

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.

Optical Properties of Transparent Rare-Earth Doped Sol-Gel Derived Nano-Glass Ceramics

“…The investigations of the Nd 3+ -doped SiO 2 -NaLaF 4 glass ceramic showed both LaF 3 /NaLaF 4 crystalline phases for different initial compositions and annealing temperatures; the crystallization of NaLaF 4 was only promoted for Na deficiency in the precursors and higher temperatures calcination, above 650 • C [68]. The incorporation of Nd 3+ ion into NaLaF 4 and LaF 3 nanocrystals was confirmed by site-selective emission and excitation spectra (Figure 16).…”

“…The sol-gel route has been used to obtain other transparent glass ceramic compositions comprising thernary fluoride nanocrystalline Me1Me2F4 phases such as: SiO 2 -NaYF 4 [67], SiO 2 -NaLaF 4 [68], SiO 2 -NaGdF 4 [69], SiO 2 -KLaF 4 [70], SiO 2 -KYF 4 [71], SiO 2 -LiYF 4 [30,72,73] and their properties have been investigated. In these cases, the crystallization mechanism seems to be more complicated and the decomposition of metal trifluoroacetates is likely to be accompanied by some chemical reaction between metal and fluorine partners, followed by nanocrystalline phase precipitation within the glassy matrix.…”

“…In these cases, the crystallization mechanism seems to be more complicated and the decomposition of metal trifluoroacetates is likely to be accompanied by some chemical reaction between metal and fluorine partners, followed by nanocrystalline phase precipitation within the glassy matrix. It was observed that the nature of the final precipitate crystalline phase is strongly dependent on the molar ratio between trivalent ion (Y, Gd, La) and alkali metals ions (Li, Na or K), and in general mixtures of fluorides were obtained (for LaF-NaLaF 4 [68] and YF 3 -LiYF 4 [30,72,73]) or different phase mixtures of the same compound (cubic and/or hexagonal NaGdF 4 or KLaF 4 nanocrystals [69,70]). Hence, an optimization of the initial composition and processing parameters (time and temperature) was required to obtain precipitation of the desired crystalline phase.…”

Tailor-made Tenorite (CuO) Interface Films for Enhanced Photocatalysis: An Improved Dip-Coating Approach with Enhanced Surface Topography and Hydrophobicity

“…Thin films are sol-gel applications with several functions (Althamthami et al 2022) that provide more flexibility in terms of lower sintering temperatures depending on precursors, reduced cost, improved compositional control, increased bioactivity, and improved coating morphological control (Ahmadi and Afshar 2021;Singh et al 2022). It may also be readily synthesized utilizing sol-gel spin-coating or dip-coating procedures, which are complex or impossible to do using conventional synthetic methods (Wang and Bierwagen 2009;Cruz et al 2021;Inkrataitė et al 2022). Furthermore, the resulting material can offer good transparency, mechanical qualities, and a high refractive index.…”

Glass-Ceramics: Improving Glass Properties through Crystallization

“…A continuous trap distribution was obtained, making this material promising for use as a radiation sensor or in spectral converters. The second published work on this field is that of Cruz et al [2], which shows the nanocrystallization of LaF 3 and NaLaF 4 in SiO 2 matrices prepared by the sol-gel route. In addition to LaF 3 , NaLaF 4 crystallizes only at the highest treatment temperature and the NaLaF 4 crystal fraction was changed by tuning the amount of Na.…”