Xiuqing Zhou

Controlled synthesis and morphology dependent luminescence of Lu2O2S:Eu3+ phosphors

Lu2O2S:Eu3+ phosphors were successfully prepared with controllable morphology, including 3D sphere-like, cloud-like, nested tetrahedron, flower-like and 1D rod-like architectures. It is indicated that the pH value of the system plays an important role in the morphology and the degree of crystallinity of the product. Interestingly, with morphological changes, the band gap energy of the Lu2O2S crystal changed, followed by a variation of the crystal field symmetry and furthermore the luminescence performance. Therefore, such a morphology-sensitive luminescence property was first interpreted in terms of degree of crystallinity, band gap energy, and the crystal field symmetry around Eu3+.

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.

Facile synthesis and color-tunable properties of BaLuF5:Ce,Tb,Eu(Sm) submicrospheres via a facile ionic liquid/EG two-phase system.

BaLuF5:Ce,Tb,Eu(Sm) submicrospheres were synthesized via an ILs/ethylene glycol(EG) two-phase system. The crystalline phase, size, morphology, and luminescence properties were characterized using powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra. The results show that 1-methyl-3-octylimidazolium hexafluorophosphate ([Omim]PF6) was used as fluoride source and capping agent to tune morphology and size of the crystals. The formation mechanism has been supposed. Under the excitation of ultraviolet, the BaLuF5:5%Ce3+,5%Tb3+, BaLuF5:Eu3+, and BaLuF5:5%Ce3+,5%Sm3+ exhibit green and red emission, which was derived from Tb3+, Eu3+, and Sm3+ emission. When codoping Ce3+, Tb3+, Sm3+ or Eu3+ together, multi-color emission can be realized. Furthermore, this synthetic route may have potential applications for fabricating other lanthanide fluorides.

Ionic liquids assisted synthesis and luminescence properties of Ca5(PO4)3Cl:Ce3+,Tb3+ nanostructures

Ca5(PO4)3Cl straw-like sheaves and microrods were synthesized via a ionic liquids based hydrothermal method. The ionic liquids [Omim]Cl was utilized to introduce a new chloride source. The influences of the ionic liquids amount and reaction time on the final products were investigated in detail. A possible splitting formation mechanism for the interesting architectures has been proposed to interpret the growth process. The optical properties of the Ca5(PO4)3Cl:Ce3+,Tb3+ phosphor with different morphology have been discussed. This ionic liquids based hydrothermal method is a novel and facile route for the synthesis of other apatite phosphors.

Lu2O2S:Tb3+, Eu3+ nanorods: luminescence, energy transfer, and multicolour tuneable emission

A series of Tb3+ and Eu3+ singly-doped and co-doped rod-like Lu2O2S phosphors have been synthesized via a facile hydrothermal method followed by a subsequent calcination process. The phosphors, with excellent dispersion and uniform rods, exhibit the characteristic Tb3+ or/and Eu3+ emissions with the strongest peaks located at 544 nm (green) and 626 nm (red), respectively. Moreover, the emission intensities of both Tb3+ and Eu3+ remarkably vary with increasing Eu3+ incorporation, and as a result, bright and tunable color emission can be realized in the single-phase Lu2O2S host by varying the ratio of Eu3+ to Tb3+ ions. In addition, the multicolor luminescence of Tb3+ and Eu3+ co-doped rod-like Lu2O2S phosphors can be readily achieved by changing the excitation wavelengths. The energy transfer from Tb3+ to Eu3+ ions in Lu2O2S was systematically investigated in detail. These results prove that the as-synthesized Lu2O2S nanorods are an excellent host for rare earth luminescence, and the Lu2O2S:Tb3+, Eu3+ nanorods with tunable multicolor luminescence properties may have potential applications in the fields of full-color displays, solid-state light and field emission displays.

One-pot synthesis of hydrophobic and enhanced red-emitting CaCO3:Eu3+ phosphors

Enhanced red-emitting CaCO3:Eu3+ phosphors were in situ prepared using the carbonization method in the presence of sodium oleate. It has been proved that the introduction of sodium oleate can endow the products with a hydrophobic surface, which makes the products exhibit good compatibility with plastics or other polymers. Remarkably, the addition of sodium oleate can also enhance the red emission intensity of CaCO3:Eu3+ phosphors greatly compared to that of the common CaCO3:Eu3+ phosphors. The enhancement is attributed to two functions of sodium oleate. One function is that sodium oleate can avoid OH ligands and/or crystal water molecules attached on the surface of CaCO3 particles; the other function is that Na+ ions can supply effective charge compensation.

Morphology control and tunable color of LuVO4:Ln3+ (Ln = Tm, Er, Sm, Eu) nano/micro-structures

LuVO4:Eu3+ nano/microcrystals with different morphologies/sizes including nanoparticles, nanosheets, nanodisks, nanoquadrangles, sub-microflakes, microspheres, and bulks were successfully synthesized by a mild solvothermal process using tartaric acid (TA) as the template. The amount of tartaric acid (TA) and the initial pH value play vital roles in controlling the morphologies of LuVO4 products. Besides, the reaction temperature was responsible for the generation of pure LuVO4 crystals in the presence of TA. Based on this, the possible formation mechanism of multi-morphologies was proposed. Furthermore, the dependence of luminescence performance on morphology has been discussed in detail. The LuVO4:Ln3+ (Ln = Tm3+, Er3+, Sm3+, Eu3+) nanoparticles show the characterized transition of Ln3+ and give bright blue, green, orange-red and red emission. Moreover, blue-green, green-yellow, pink, yellow-pink and white light can be obtained by adjusting the amount of doped Ln3+ ions and the corresponding concentrations of the LuVO4 host. This general and simple method may be of much significance in the synthesis of many other rare earth inorganic materials.

Electrospinning fabrication and luminescence properties of Lu2O2S:Eu3+ fibers

Luminescent one-dimensional Lu2O2S:Eu3+ fibers were successfully prepared via an electrospinning method followed by a subsequent two-step calcination process for the first time. Scanning electron microscopy (SEM) showed that the as-obtained samples present a fiber-like morphology with uniform size and the diameters of the fibers changed from microscale to nanoscale with the increase of Eu3+ concentration. The emission spectra indicated that the obtained Lu2O2S:Eu3+ fibers exhibited typical Eu3+ (5D0–7FJ) red emission under ultraviolet excitation and the concentration quenching effects occurred in the fibers composed of 3 mol% Eu3+. The decay kinetics behaviors of the Lu2O2S:Eu3+ fibers were investigated, which showed that the fibers composed of 3 mol% Eu3+ also had the longest lifetime. The spectral characteristics and Eu–O ligand behavior were discussed through Judd–Ofelt parameters such as intensity parameters (Ω2, Ω4), radiative transition probability (ARAD), radiative lifetime (τrad), and branching ratio (β0J). In addition, the energy-dispersive X-ray spectra (EDS), thermogravimetry-differential thermal analysis (TG-DTA) and the formation mechanism were also displayed in order to better understand the work.