Ruiqing Li

Facile synthesis of Ag/ZnO micro-flowers and their improved ultraviolet and visible light photocatalytic activity

Three-dimensional (3D) flower-like Ag/ZnO heterostructures with different Ag content were prepared using a facile two-step method. The samples structure, morphology and optical properties were well-characterized using XRD, SEM, EDS, XPS, DRS, PL and ICP-AES techniques. The results demonstrated the successful deposition of Ag nanoparticles on a flower-like ZnO surface. The photocatalytic performance was evaluated by the photocatalytic degradation of rhodamine B (RhB) under ultraviolet and visible light. The results showed that the Ag/ZnO heterostructures had superior photocatalytic activity compared to the pure ZnO samples and the commercial photocatalyst TiO2 (Degussa, P25). The enhanced photocatalytic activity was attributed to the effective separation of electron/hole pairs on flower-like ZnO by employing Ag nanoparticles as a conductor. Furthermore, 3D flower-like Ag/ZnO microspheres exhibited good recycling stabilities over several separation cycles photodegradation.

Tunable luminescence properties of the novel Tm3+- and Dy3+-codoped LiLa(MoO4)x(WO4)2−x phosphors for white light-emitting diodes

A series of Tm3+- and Dy3+-codoped LiLa(MoO4)x(WO4)2−x phosphors were prepared via the conventional solid-state reaction method. It was discovered that the optimum single doped concentrations of both Tm3+ and Dy3+ are 0.04 for the LiLa(WO4)2 host; moreover, LiLa(WO4)2:0.04Tm3+ and LiLa(WO4)2:0.04Dy3+ emit blue and yellow light, respectively. On the other hand, the emission colors of Tm3+- and Dy3+-codoped LiLa(WO4)2 could be tuned from blue to white by tuning the energy transfer. With increase in the Dy3+ doped concentration, the energy transfer efficiency of LiLa(WO4)2:0.005Tm3+,yDy3+ increased gradually and reached as high as 88% when the concentration of Dy3+ was 0.05. The energy transfer from Tm3+ to Dy3+ was revealed to be resonant via the quadrupole–quadrupole mechanism. As for LiLa(MoO4)x(WO4)2−x:0.005Tm3+,0.03Dy3+ phosphors, the emission intensities of both Tm3+ and Dy3+ were found to reach a maximum when the molar ratio of Mo/W was 0:2. In addition, with increase in the proportion of MoO42−, the location of the chromaticity coordinates changed from the edge to the center of the white area. When the relative ratio of Mo/W was 2:0, the chromaticity coordinates were much closer to the standard chromaticity coordinates for white light. The results indicate that these phosphors may have potential applications in the fields of UV-excited white light-emitting diodes.

Preparation of porous 3D Ce-doped ZnO microflowers with enhanced photocatalytic performance

Porous 3D Ce-doped ZnO microflowers were prepared by a hydrothermal method followed by a low temperature annealing process. The effects of Ce doping on the structural and photocatalytic properties of porous ZnO microflowers were investigated in detail. The samples were characterized using XRD, SEM, EDS, XPS, DRS, PL spectra and BET surface area measurements. According to the XRD analysis, both of the crystalline structures of the synthesized pure ZnO and Ce-doped ZnO samples are hexagonal wurtzite. The XPS results demonstrated the successful synthesis of Ce4+ doped ZnO. In addition, the SEM morphologies showed the unique porous 3D flower-like structure of the Ce-doped ZnO. Compared with the porous ZnO microflowers, the Ce-doped ZnO samples exhibit improved photocatalytic performance in the decomposition of Rhodamine B (RhB). It is proposed that the special structural feature with a porous 3D structured and Ce modification lead to the rapid photocatalytic activity of the Ce-doped ZnO microflowers.

Shape controllable synthesis and multicolour fluorescence of lanthanide doped Vernier yttrium oxyfluoride

A series of Tb3+ and Eu3+ activated orthorhombic yttrium oxyfluoride, Y7O6F9 (denoted as V-YOF hereafter) phosphors were synthesized through a facile two-step hydrothermal synthesis route followed by heat treatment for the first time. The phase, morphologies, sizes and photoluminescence properties of as-prepared samples were investigated by means of XRD, SEM, and luminescence spectroscopy. A series of characteristic emission originated from the f–f transitions of Eu3+ and Tb3+ can be observed and multicolour emissions from green to yellow and then to red have been achieved in the V-YOF:Tb3+,Eu3+ samples under 378 nm irradiation. The energy transfer process from Tb3+ to Eu3+ was studied and demonstrated to be a quadrupole–quadrupole interaction mechanism. These results show that the V-YOF phosphors have potential applications in field-emission displays.

Self-assembled 3D sphere-like SrMoO4 and SrMoO4:Ln3+ (Ln = Eu, Sm, Tb, Dy) microarchitectures: Facile sonochemical synthesis and optical properties

Three-dimensional (3D) well-defined SrMoO4 and SrMoO4:Ln(3+) (Ln=Eu, Sm, Tb, Dy) hierarchical structures of obvious sphere-like shape have been successfully synthesized using a large-scale and facile sonochemical route without using any catalysts or templates. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and photoluminescence (PL) spectra were used to characterize the samples. The intrinsic structural feature of SrMoO4 and external factor, namely the ultrasonic time and the pH value, are responsible for the ultimate shape evolutions of the product. The possible formation mechanism for the product is presented. Additionally, the PL properties of SrMoO4 and SrMoO4:Ln(3+) (Ln=Eu, Sm, Tb, Dy) hierarchical structures were investigated in detail. The Ln(3+) ions doped SrMoO4 samples exhibit respective bright red-orange, yellow, green and white light of Eu(3+), Sm(3+), Tb(3+) and Dy(3+) under ultraviolet excitation, and have potential application in the field of color display. Simultaneously, this novel and efficient pathway could open new opportunities for further investigating about the properties of molybdate materials.

Morphology control and multicolor-tunable luminescence of YOF:Ln3+ (Ln = Eu, Tb, Dy, Tm) nano-/microcrystals

YOF:Ln3+ (Ln = Eu, Tb, Dy, Tm) nano-/microcrystals with high uniformity, monodispersity and a variety of well-defined morphologies, such as submicro spheres, ellipsoids, nanorods, microspindles and spindle nanorod bundles, have been successfully synthesized via a urea based homogeneous precipitation method followed by a heat-treatment process. The influence of pH values, fluoride sources and reaction time on the sizes and morphologies of the as-prepared precursor was systematically investigated and discussed. The possible formation mechanism for the precursor has been presented. Upon ultraviolet excitation, the YOF:Ln3+ (Ln = Eu, Tb, Dy, Tm) submicro spheres show their characteristic f–f emissions and give red, green, yellow, and blue emission, respectively. Moreover, a novel single-phased and near-UV-pumped white-light-emitting phosphor YOF:Tm3+,Dy3+ was also successfully fabricated by singly varying the doping content of Dy3+ with a fixed Tm3+ content through the principle of energy transfer. This merit of multicolor emissions in the visible region endows materials of this kind with potential application in field-emission display devices and white light-emitting diodes.

Rapid, morphology-controllable synthesis of GdOF:Ln3+ (Ln = Eu, Tb) crystals with multicolor-tunable luminescence properties

In this paper, GdOF crystals with high uniformity, monodispersity and a variety of well-defined morphologies, such as spheres, nanorods, and nanorod bundles have been successfully synthesized via the urea based homogeneous precipitation method followed by a heat treatment. The influence of pH values, fluoride sources and reaction time on the sizes and morphologies was systematically investigated and discussed. The possible formation mechanism for the precursor has been presented. Under ultraviolet excitation, the GdOF:Ln3+ (Ln = Eu, Tb) submicron spheres show their characteristic f–f emissions and give red, and green emissions, respectively. Moreover, for Tb3+/Eu3+ co-doped GdOF phosphors, tunable emissions have been obtained and the color tones can be tuned from green, through yellow, and then to red by simply adjusting the doping Eu3+ concentrations. This merit of multicolor emissions in the visible region makes these materials hold great promise for applications in field-emission displays.

Morphology-controllable synthesis of LaOF:Ln(3+) (Ln=Eu, Tb) crystals with multicolor luminescence properties.

In this paper, well defined LaOF crystals with multiform morphologies were first prepared via the urea-based precipitation method followed by a heat treatment. The morphologies of the LaOF samples, including nanospheres and nanorods, can be easily modulated by changing the fluorine sources. XRD, FT-IR, SEM, TEM, and emission spectra were used to characterize the prepared samples. Under ultraviolet excitation, the LaOF:Ln(3+) nanospheres display the characteristic f-f transitions of Ln(3+) (Ln=Eu, Tb) ions and give bright red, and green emissions, respectively. Furthermore, by codoping the Tb(3+) and Eu(3+) ions into LaOF host and varying the doping concentration of the Eu(3+) ions, multicolor tunable emissions have been obtained under the irradiation of 379nm. These results show this material may have potential applications in field-emission displays.

Phase transition, morphology transformation and highly enhanced luminescence properties of YOF:Eu3+ crystals by Gd3+ doping

A series of undoped and Eu3+ doped YOF and Y1−xGdxOF (x = 0–0.7) crystals were prepared via a urea based homogeneous precipitation method followed by a heat treatment process. After Gd3+ doping, we observed the crystal phase transition, morphology transformation, and greatly enhanced luminescence properties of the YOF crystals. The results reveal that the addition of Gd3+ can promote the phase transition from the hexagonal phase to the rhombohedral phase and the morphology transformation from spheres, though a mixture of rods and spheres, to spheres. The luminescence properties of Eu3+ doped YOF phosphors were investigated upon UV excitation and the quenching concentration of Eu3+ was found to be 10 mol%. More importantly, the luminescence intensity after doping a certain amount of Gd3+ increased by 31 times compared to that of the Gd3+ free sample, which may be due to the modification of the crystal field and the crystal phase of YOF, providing an effective way to gain numerous Gd3+ doped luminescent materials. These results show that the Gd3+ doped red phosphors have potential applications in white light emitting diodes.