Luminescent properties of single-phase Ba2-x-1.5y-1.5z P2 O7 :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.

The luminescence properties of Sr2-1.5x-1.5y P2 O7 :xDy3+ ,yCe3+ phosphor for near-UV-based white LEDs synthesized by a chemical co-precipitation method.

A series of Sr2 P2 O7 :Dy3+ , Sr2 P2 O7 :Ce3+ and Sr2 P2 O7 :Dy3+ ,Ce3+ phosphors was synthesized via the one-step calcination process for the precursors prepared by co-precipitation methods. The phases, morphology, quantum efficiency and photoluminescence properties of the obtained phosphors were characterized systematically. These results show that the near-spherical particles prepared through calcining the precursors by means of ammonium dibasic phosphate co-precipitation (method 3) have the smallest particle size and strongest emission intensity among the three methods in the paper. With Dy3+ concentration increasing in Sr2 P2 O7 :Dy3+ phosphors, the luminescence intensity first increases, reaches maximum, and then decreases. A similar trend was followed by Sr2 P2 O7 :Ce3+ with Ce3+ concentration increasing. A successful attempt was made to initiate the energy transfer mechanism from Ce3+ to Dy3+ in the host lattice and an overlap between the emission band of Ce3+ and the excitation band of Dy3+ indicated that the Ce3+  â†’ Dy3+ energy transfer may indeed exist. It is clear that the photoluminescence intensity of Dy3+ as well as the quantum efficiency of the phosphor can be enhanced markedly by co-doping Ce3+ . Sr2 P2 O7 :Dy3+ ,Ce3+ has its (CIE) chromaticity coordinates in the bluish-white-light region, near the standard illuminant D65 . The CIE 1913 chromaticity coordinates of Sr2 P2 O7 :Dy3+ phosphors fall in the white-light region, and are adjacent to the ideal white-light coordinates. In addition, the colour temperature and colour tone of Sr2 P2 O7 :Dy3+ could be adjusted by changing the relative concentration of Dy3+ . In short, Sr2 P2 O7 :Dy3+ can be a promising single-phased white-light emitting phosphor for near-UV (NUV) w-LEDs.

The luminescent properties and crystal structure of Sr(1.5-x)-(1.5y) Mg0.5 SiO4 :xEu2+ ,yCe3+ blue phosphor synthesized by co-precipitation method.

In order to improve the luminescent performance of silicate blue phosphors, Sr(1.5-x)-(1.5y) Mg0.5 SiO4 :xEu2+ ,yCe3+ phosphors were synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. The crystal structure and luminescent properties of the phosphors were analyzed using X-ray diffraction and fluorescence spectrophotometry, respectively. Because the activated ions (Eu2+ ) can occupy two different types of sites (Sr1 and Sr2 ), the emission spectrum of Eu2+ excited at 350 nm contains two single bands (EM1 and EM2 ) in the wavelength range 400-550 nm, centered at 463 nm, and the emission intensity first increases and then decreases with increasing concentrations of Eu2+ ions. Co-doping of Ce3+ ions can greatly enhance the emission intensity of Eu2+ by transferring its excitation energy to Eu2+ . Because of concentration quenching, a higher substitution concentration of Ce3+ can lead to a decrease in the intensity. Meanwhile, the quantum efficiency of the phosphor is improved after doping with Ce3+ , and a blue shift phenomenon is observed in the CIE chromaticity diagram. The results indicate that Sr(1.5-x)-(1.5y) Mg0.5 SiO4 :xEu2+ ,yCe3+ can be used as a potential new blue phosphor for white light-emitting diodes.