Meiqi Chang

Dendrimer-based preparation and luminescence studies of SiO2 fibers doping Eu3+ activator in interstitial sites

Luminescent one-dimensional Eu3+ doped SiO2 fibers have been readily prepared by electrospinning method combined with a sol–gel process. In this work, polyvinylpyrrolidone (PVP) as a simple commercial dendrimer not only increased the viscosity of solution but also provided weak hydrogen bonds with silica, which was significant in improving the electrospinability. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the as-obtained samples present fiber-like morphology with uniform size and the diameters of fibers became wider with the increase of Eu3+ concentration, from nanoscale to microscale. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicated that Eu3+ activator ions have been doped into the interstitial sites of SiO2 fibers through the electrostatic interaction, which would reduce the symmetry of SiO2 framework. The photoluminescence (PL) properties include the diffuse reflectance, excitation and emission spectra indicated that the obtained SiO2:Eu3+ fibers exhibited typical Eu3+ (5D0–7FJ) red emission under ultraviolet excitation and the band energy was changed due to the doping of stable Eu3+ activator ions. Meanwhile, the concentration quenching effects and decay kinetics behaviors of SiO2:Eu3+ fibers were investigated and the optimal doping concentration and the longest lifetime were both in the composition of 16 mol% Eu3+. In addition, the energy-dispersive X-ray spectrum (EDS), thermogravimetry differential thermal analysis (TG-DTA) and the formation mechanism were also displayed in order to better understand the work.

Luminescence properties and Judd–Ofelt analysis of TiO2:Eu3+ nanofibers via polymer-based electrospinning method

One-dimensional TiO2:xEu3+ nanofibers were fabricated via electrospinning and subsequent calcination. The as-spun nanofibers were calcined at 600, 700, 800 and 900 °C for 5 h at a heating rate of 1 °C min−1 and the concentrations of Eu3+ dopants were varied from 17 mol% to 20 mol%. The TiO2:19 mol% Eu3+ nanofibers which calcined at 700 °C (optimum condition) were investigated by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray photo-electronic spectroscopy (XPS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL) excitation and emission spectra. In this article, we have discussed the effect of different calcination temperature on fiber diameter and photoluminescence properties of europium doped titania (TiO2:xEu3+) nanofibers. The possible formation mechanism of TiO2:x mol% Eu3+ nanofibers was also discussed. The spectral characteristics and Eu–O ligand behavior were discussed through Judd–Ofelt parameters such as radiative transition probability (ARAD), radiative lifetime (τrad), branching ratio (β0J) and intensity parameters (Ω2, Ω4). Furthermore, the TiO2:19 mol% Eu3+ nanofibers exhibit strong red luminescence that corresponds to the 5D0–7F2 transition (612 nm) of the Eu3+ ions under the excitation of ultraviolet light.

Hydrothermal assisted sol–gel synthesis and multisite luminescent properties of anatase TiO2:Eu3+ nanorods

Uniform TiO2:Eu3+ spindlelike nanorods have been successfully prepared by a hydrothermal assisted sol–gel process with ethanediamine (ED) as the shape controller. A possible formation mechanism and luminescent properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) and kinetic decays. Site-selective spectroscopy was used to research into sites of Eu3+ in TiO2 lattice at 10 K, which identifies two kinds of sites of Eu3+ in TiO2 nanocrystals. One is located in the distorted lattice sites near the surface, and the other is situated in lattice sites with ordered crystalline environment. Moreover, the luminescence decay curve of products further proved the existence of multiple sites of Eu3+ ions in TiO2 nanocrystals.

Magnetic-downconversion luminescent bifunctional BaGdF5:Dy3+,Eu3+ nanospheres: energy transfer, multicolor luminescence and paramagnetic properties

A series of Dy3+ or/and Eu3+ doped cubic BaGdF5 phosphors were synthesized for the first time by an L-arginine hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopies (PL) and luminescence decay. The results indicate that the as-prepared samples are a pure cubic phase of BaGdF5, taking on irregular nanoparticles with an average size of 20 nm. The as-prepared Dy3+ or Eu3+ single doped samples show strong blue and red emissions, originating from the 4F9/2 → 6H15/2 transition of the Dy3+ ions and the 5D1 → 7FJ (J = 1, 2) and 5D0 → 7FJ (J = 1, 2, 4) transition of the Eu3+ ions. Based on the rare earth concentrations and excitation wavelengths, multiple (white, red, blue and green yellow) emissions are obtained by Eu3+ ion co-activated BaGdF5:Dy3+ phosphors. In addition, the energy migration from Dy3+ to Eu3+ has been reported in detail. Furthermore, the obtained samples also exhibit paramagnetic properties at room temperature and low temperature. It is obvious that Dy3+, Eu3+ co-doped BaGdF5 nanomaterials with tunable multicolor emissions may have potential application in the field of full-color displays.