Li Yongxiu

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.

Enhancement of photoluminescence of Ba2SiO4:Eu2+ by co-doping of La3+ or Y3+

Abstract Green light-emitting Ba 2 SiO 4 :Eu 2+ phosphors co-doped with La or Y were synthesized by conventional solid-state reaction technique in reductive atmosphere (a mixture of 5% H 2 and 95% N 2 ). The results showed that the co-doping of La and Y could greatly enhance the fluorescence intensity of Ba 2 SiO 4 :Eu 2+ phosphors. The optimum doping concentration expressed by the x value in (Ba 0.985–1.5 x RE x ) 2 SiO 4 : 0.03Eu 2+ (RE=La or Y) was determined to be of 0.05. The excitation and emission peaks of all as-synthesized phosphors were wide bands. The excitation bands ranged from 250 to 400 nm, which matched well with the wavelength of near ultraviolet white light-emitting diodes (LED) chip and could be used as a potential candidate for the fabrication of white LED. The emission bands from 450 to 550 nm were typical 5d–4f transition emission of Eu 2+ and displayed un-symmetry profiles because of the two substitution sites of Ba 2+ with Eu 2+ .

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.

Fabrication and ultraviolet-shielding properties of silica-coated titania-doped ceria nanoparticles

Abstract A series of well-dispersed titania-doped ceria nanoparticles Ce 1- x Ti x O 2 were rapidly prepared by a novel salt-assisted solution combustion process using correspondent metal nitrates as oxidizers and ethyl glycol as fuel, and then coated with amorphous silica by seeded polymerization using tetraethyl orthoslicate (TEOS). The as-prepared samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy. The results indicated that compared with the as-prepared pure ceria nanoparticles, the red-shift phenomenon occurred for Ti-doped ceria nanoparticles with Ti incorporation. Meanwhile, the absorption intensity in the UV light region slightly decreased and transmission rate in visible light region was somewhat enhanced. In comparison with the silica-coated CeO 2 nanopowders, the silica-coated Ce 0.95 Ti 0.05 O 2 nanopowders displayed the same absorption intensity in the UV light region, broader UV absorption band and higher transmission rate in visible light region.