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.

In this study, glass-ceramics based on Sr₂MgSi₂O₇ phosphor co-doped with Eu/Dy were obtained from the sintering and crystallisation of glass powders. The glasses were melted in a gas furnace to simulate an industrial process, and the dopant concentration was varied to optimise the luminescence persistence times. The doped parent glasses showed red emission under UV light excitation due to the doping of Eu³⁺ ions, while the corresponding glass-ceramics showed persistent blue emission corresponding to the presence of Eu²⁺ in the crystalline environment. The dopant concentration had a strong impact on the sintering/crystallisation kinetics affecting the final glass-ceramic microstructure. The microstructures and morphology of the crystals responsible for the blue emission were observed by scanning electron microscopy–cathodoluminescence. The composition of the crystallised phases and the distribution of rare-earth (RE) ions in the crystals and in the residual glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis. The emission and persistence of phosphorescence were studied by photoluminescence.

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.

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 T_g + 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.

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO₂-20(1.5Eu³⁺: NaGdF₄) were prepared with sol-gel following the “pre-crystallised nanoparticles route” with promising optical results. The preparation of 1.5 mol % Eu³⁺-doped NaGdF₄ nanoparticles, named 1.5Eu³⁺: NaGdF₄, was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO₂-20(1.5Eu³⁺: NaGdF₄) OxGCs prepared from these nanoparticles’ suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF₄ crystalline phases. The optical properties of both nanoparticles’ phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the ⁵D₀ state. The emission spectra obtained by exciting the Eu³⁺-O²⁻ charge transfer band showed similar features in both cases corresponding the higher emission intensity to the ⁵D₀→⁷F₂ transition that indicates a non-centrosymmetric site for Eu³⁺ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu³⁺ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.

In this work, the existence of different crystal field sites for the rare-earth-doped tin dioxide nanopowder and RE-doped SiO2-SnO2 glass-ceramics is investigated. The slightly different crystal field symmetries have been resolved by using site-selective fluorescence line-narrowing spectroscopy. The obtained results show that a variety of optically non equivalent sites exist for the europium ion in the tin dioxide oxide structure associated to different allowed positions of the oxygen vacancies, whereas additional spectral disorder is found in the case of the glass-ceramic matrix. Ultrafast spectroscopy performed on Eu³⁺-doped tin dioxide nanocrystals shows that host-rare earth energy transfer occurs at a transfer rate of about 1.5×10⁶ s^-1. Similar experiments carried out for the Er³⁺-doped glass-ceramic system also validate the hypothesis that both host and matrix-excited RE emissions are decoupled due to the different origins of the involved physical mechanisms.