Dachuan Zhu

Synthesis and Luminescence Properties of (Y, Gd) (P, V)O4:Eu3+, Bi3+Red Nano-phosphors with Enhanced Photoluminescence by Bi3+, Gd3+ Doping

A series of (Y1−y, Gdy)0.95−x(Py, V1−y)O4:0.05Eu3+, xBi3+ phosphors have been successfully prepared by a subsection method. The crystal structure, surface morphology and luminescence properties were investigated. It was found that the sintered samples crystallized in a tetragonal crystal system with space group I41/amd(a = b = 0.7119 nm, c = 0.6290 nm). The products presented rod-like morphology with length of 100–150 nm and width of 50–100 nm. A maximum peak at 619 nm (5D0 →7F2) was observed in emission spectrum of the phosphors. It was also found that co-doping of Bi3+, P5+ and Gd3+ions into YVO4:Eu3+ can not only made the right edge of the excitation band shift to the long-wavelength region, but also increased the emission intensity at 619 nm sharply and decreased the lifetime of fluorescence decay. These results may expand the application scope of the phosphors.

A novel near-ultraviolet (NUV) converting blue-violet Ca2−xAlMg0.5Si1.5O7:xCe3+ phosphor for white light-emitting-diodes (w-LEDs)

Ce3+ doped aluminosilicate phosphors (Ca2−xAlMg0.5Si1.5O7:xCe3+, x = 0.015–0.075) for white NUV w-LEDs were synthesized by a solid-state reaction method at 1250 °C. The as-prepared samples were characterized by XRD and fluorescence spectrophotometry; the obtained XRD results show that the target phase was synthesized and doping with Ce3+ did not result in an impurity phase. The as-prepared phosphors exhibit a strong blue-violet emission under the near-ultraviolet radiation excitation. Corresponding fitting results show the emission spectra contain two distinct single bands, which come from the transition of 2D3/2 → 2F7/2 and 2F5/2 of the Ce3+ ion. The colorimetric coordinates of the sample with x = 0.03 are (0.1574, 0.0359), located in the blue-violet region. In addition, the sample exhibits high external quantum efficiency (EQE = 37.3%) and excellent thermal stability (T50 = 230 °C). We obtained bright blue-violet light by pumping the sample with NUV light (λ ≈ 365 nm), which suggests that this material has the potential for application as a NUV converting blue-violet phosphor for the NUV w-LEDs.

Highly ordered Ag–TiO 2 nanocomposited arrays with high visible-light photocatalytic activity

TiO2 is active only in the ultraviolet region. To enhance the active ability, a combined method consisting of the anodic oxidation method and the hydrothermal method was developed to prepare highly ordered Ag-TiO2 nanocomposited arrays. The anodic oxidation was used to synthesize amorphous nanotubes with high chemical activity that subsequently served as highly ordered templates in preparing the final sample. The amorphous nanotubes got converted to highly ordered Ag-TiO2 (anatase) arrays in the silver nitrate & glucose aqueous solution via hydrothermal treatment. SEM and TEM results show that the Ag-TiO2 nanocomposite was composed of a large number of Ag nanoparticles and anatase TiO2 nanoparticles, and the morphology of those at the top of the arrays was found different from that of its trunk. The morphology evolution mechanism of the obtained sample was discussed. It is also revealed that the Ag-TiO2 nanocomposite has high visible-light photocatalytic activity.

Luminescent properties of single‐phase Ba2‐x‐1.5y‐1.5zP2O7:xEu2+,yCe3+, zTb3+ phosphors for white light‐emitting diode

A series of Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors was synthesized via a co-precipitation method, then their crystal structure, quantum efficiency and luminescent properties were analyzed by XRD and FL, respectively. The results showed that these phosphors not only presented the excitation characteristics of Ba2 P2 O7 :xEu2+ ,zTb3+ , but also exhibited that of the Ba2 P2 O7 :yCe3+ ,zTb3+ phosphor. Meanwhile, the tri-doped phosphor showed a stronger absorption around 320 nm in contrast with the Eu2+ /Ce3+ :Tb3+ co-doped phosphor. Not only can energy transfer from Ce3+ →Eu2+ be observed; the energy transfer mechanism from Eu2+ to Tb3+ is discussed in the tri-doped system. Ce3+ affects the luminescence properties of Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors just as the sensitizer whereas Eu2+ is considered both as the sensitizer and the activator. The chromaticity coordinates of tri-doped phosphors excited at 320 nm stayed steadily in the bluish-white light region,and the emitted color and color temperature (CCT) of these phosphors could be tuned by adjusting the relative contents of Eu2+ , Ce3+ and Tb3+ . Hence, the single phase Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors may be considered as potential candidates for white light-emitting diodes.

Effect of sintering temperature on the emission-spectrum-shape-evolution of Sr 2 SiO 4 :Eu 2+ phosphor

Color rendering index and color temperature are the key factors for the LEDs application. The two points are closely related to the emission spectrum shape of phosphors. As the key factors for the LEDs application, both the above aspects are closely dependent on the emission spectrum shape of phosphors. In this study, the emission spectrum shape has been adjusted via a home designed route. A combination of structural, morphological, and optical characterization techniques has been used to study the shape evolution mechanism. The structural results show that the Sr2SiO4 phase has not been changed with the sintering temperature increasing, but the emission spectrum shape has changed dramatically, meanwhile, the colorimetric coordinate moves from blue-green to green region. Gaussian fitting method has been used to treat the emission spectrum, and the as-obtained results indicate the emission spectrum contains two single bands, which come from the 4f7(7S7/2)–4f6(7FJ)5d1 transition of Eu2+ on the different Sr sites in the Sr2SiO4 crystal. The intensity of the two single bands is driven by sintering temperature, because of the difference between the energy barrier of the Eu2+ occupying the different Sr sites in the matrix crystal. Moreover, the mechanism of the above phenomenon has also been studied by means of first principles method, and the obtained results agree well with the former deduction.