Abstract
CaF2:Eu3+ glass-ceramic sol-gel materials have been examined for reddish-orange photoluminescence applications. The transformation from precursor xerogels to glass-ceramic materials with dispersed fluoride nanocrystals was verified using several experimental methods: differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR-ATR), energy dispersive X-ray spectroscopy (EDS) and photoluminescence measurements. Based on luminescence spectra and their decays, the optical behavior of Eu3+ ions in fabricated glass-ceramics were characterized and compared to those of precursor xerogels. In particular, the determined luminescence lifetime of the 5D0 excited state of Eu3+ ions in nanocrystalline CaF2:Eu3+ glass-ceramic materials is significantly prolonged in comparison with prepared xerogels. The integrated intensities of emission bands associated to the 5D0 → 7F2 electric-dipole transition (ED) and the 5D0 → 7F1 magnetic-dipole transition (MD) are changed drastically during controlled ceramization process of xerogels. This implies the efficient migration of Eu3+ ions from amorphous silicate sol-gel network into low-phonon energy CaF2 nanocrystals.
Highlights
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]
Transparent glass-ceramic materials containing CaF2 fluoride nanocrystals were prepared by a low-temperature sol-gel route
Thermal decomposition of Ca(CF3 COO)2 in xerogels was confirmed by using thermogravimetric analysis (TG)/differential scanning calorimetry (DSC) methods
Summary
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]. The heat-treatment process often introduces transformation from amorphous systems to transparent oxyfluoride glass-ceramic materials and rare earths play the role as optically active ions. The coordination sphere around rare earth ions changes drastically during this structural transformation, giving important contribution to the luminescence characteristics. Among binary and ternary rare-earth fluoride nanophosphors [6], calcium fluoride CaF2 belongs to the most important and perspective nanoparticles, which could be successfully formed during the heat treatment process. Synthesis, structure and properties of transparent glass-ceramics containing CaF2 nanocrystals depended critically on treating temperature
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