Xuezhen Zhou

Pr3+-doped Li2SrSiO4 red phosphor for white LEDs

Novel red phosphors, Li2Sr1–1.5xSiO4:xPr3+ (x=0.002, 0.003, 0.004, 0.005, 0.006 and 0.008), were synthesized by conventional solid state reaction and the luminescent properties were investigated. The as-prepared phosphors showed red emission at 610 nm under excitation of blue light at 452 nm, indicating that they were promising candidates for red phosphors in the fabrication of white LEDs via blue LED chips. Their excitation bands at 452, 476 and 487 nm were attributed to transitions of 3H4→3P2, 3H4→3P1+1I6, 3H4→3P0 of Pr3+ ion. The red emissions at 606 and 610 nm were originated from the 3P0-3H6 and 1D2-3H4 transitions of Pr3+. The optimum doping concentration of Pr3+ in Li2Sr1-1.5xSiO4:xPr3+ was determined to be x=0.004. With the concentration of Pr3+ over x=0.004, the fluorescence intensity of Li2Sr1-1.5xSiO4:xPr3+ decreased, indicating the concentration quenching occurred.

Hydrothermal synthesis of Y(OH)3, Y(OH)3:Eu3+ nanotubes and the photoluminescence of Y(OH)3:Eu3+,Y2O3:Eu3+

Abstract The phase and morphology transformation during the hydrothermal treating process of Y 2 O 3 was evaluated with X-ray difference (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size and specific surface area determination. The results showed that the cubic Y 2 O 3 did not transfer into hexagonal Y(OH) 3 in pure water. Therefore, pure hexagonal Y(OH) 3 with nanotube and microrod morphologies were obtained by hydrothermal treating Y 2 O 3 at 150 °C for 12 h in 15 ml of 2 mol/L NaOH solution with and without PVA or PEG. It was suggested that the characteristic preferential growth of Y(OH) 3 was attributed to the structure anisotropy of hexahedron Y(OH) 3 . The addition of PVA or PEG could promote the forming process of nanotubes by selective adsorption on different crystal planes, which altered the growth rate along different directions and resulted in the diffusion limit of constructing ions in the center top of rods. Finally, Y(OH) 3 :Eu and Y 2 O 3 :Eu nanotubes were also synthesized by using this method, and their photoluminescence properties were evaluated.

LiZnPO4:Tb3+, Ce3+ green phosphors with high efficiency

Abstract Tb 3+ and Ce 3+ co-activated LiZnPO 4 phosphors with high luminescence efficiency were synthesized by a high temperature solid-state reaction at 1000°C for 3 h. The XRD patterns, photoluminescence spectra and SEM were recorded and the effects of Tb 3+ and Ce 3+ concentration, sintering condition on the luminescent properties of as-synthesized phosphors were investigated. The emission spectra under ultraviolet (200–300 nm) radiation showed a dominant peak at 543 nm attributed to the 5 D 4 → 7 F 5 transition of Tb 3+ , which was greatly enhanced by the co-doping of Ce 3+ , indicating that there occurred an efficient non-radiative energy transfer from Ce 3+ to Tb 3+ . The optimal doping concentrations of Tb 3+ and Ce 3+ were determined to be 9% and 10%, respectively.

Searching for a high efficiency and environmental benign reagent to leach ion-adsorption rare earths based on the zeta potential of clay particles

To overcome the serious water pollution and landslides that occur in response to in situ ion-adsorption rare earths (IAREs) leaching, it is essential to identify highly efficient and environmentally benign leaching reagents. Therefore, the leaching efficiency (LE) of IAREs by different inorganic electrolytes at different concentrations was compared, and the landslides and ion releasing performance of tailings driven by water rinsing were evaluated based on the zeta potential of clay particles (CPs). It was found that the LE increased as the concentration increased for all electrolytes. A linear relationship existed between the LE of IAREs and the zeta potential of CPs for every electrolyte, but the slope values of the linear relationships differed among the electrolytes. Moreover, the LE of IAREs by aluminum sulfate solution was the highest and the slope of the linear relationship was positive. However, the zeta potential of CPs and the slope of the linear relationship for electrolytes of bivalent metal ions became negative. According to the double electric layer model, the negative zeta potential is a result of cation migration from the Stern layer to the diffusion layer, meaning that the residual electrolytes in tailings can be washed out by rain and produce a large amount of wastewater. Additionally, the high zeta potential can increase the repulsive force between particles, leading to landslides. Therefore, aluminum sulfate as a leaching agent of IAREs not only has a high LE but also can reduce the amount of wastewater and the risk of landslides.