Luminescent Properties And Application Of Aluminosilicate Phosphors For White LED

In recent years, the white light emitting diode(WLED) has received extensive attention and research because of its excellent performance. The most common way to realize white light emitting diode is the combination of the light emitting diode chip with phosphor materials. There are usually two methods: one is the combination of the blue chip and yellow phosphor Y3Al5O12:Ce, however, the defects of the high temperature quenching and low color rendering confine its application in the field of lighting. Another is to combine an ultraviolet light emitting diode chip with red, green and blue phosphors. This method can overcome the above shortcomings and has been widely used. Therefore, in order to meet the requirements of the second methods, the research and development of high stability and strong ultraviolet absorption of the three color phosphors or single-phase multicolor emitting-light phosphors is of great significance.In this paper, some tricolor and single-phase multicolor-emitting aluminosilicate phosphors excited by ultraviolet or near ultraviolet light were synthesized. Their luminescent characters, energy transfer and the application in the light emitting diode devices were studied. The main results obtained are as follows:1. The novel green phosphor Ca2Mg0.5Al Si1.5O7:Eu2+ was prepared by high temperature solid state method. Under the excitation of 368 nm, the phosphor can emit green emission at about 525 nm. The optical concentrations of Eu2+ ions and the critical distance between ions were 1.5% and 13.40 ?, respectively. The value of the thermal activation energy is 0.5432 e V, and the fluorescence lifetime of the phosphor powder is 0.57 μs. It can be a promising green phosphor for ultraviolet-excited white light emitting diode. Further, the blue-green multicolor phosphors Ca2Mg0.5Al Si1.5O7:Ce3+,Eu2+ have been synthesized by high temperature solid state reaction. The luminescent properties are studied, and the two emission peaks peaking at 409 and 525 nm in the emission spectra are attributed to the d-f electron transitions of the Ce3+ and Eu2+ ions, respectively. The energy transfer from Ce3+ to Eu2+ is studied, and it is proved that the mechanism of energy transfer is dipole-dipole. Furthermore, under the excitation of 350 nm, the phosphor Ca2Mg0.5Al Si1.5O7:Ce3+,Eu2+ can emit blue-green color light by changing the relative doping concentration ratio of Ce3+/Eu2+, indicating that the phosphors are promising blue-to-green emitting phosphors for application in phosphor-converted white light emitting diodes.2. The multicolor single-phase phosphors Ca2Mg0.25Al1.5Si1.25O7:Ce3+,Tb3+ and Ca2Mg0.25Al1.5Si1.25O7:Ce3+,Eu2+ were prepared. The energy transfer of Ce3+ to Eu2+ and Ce3+ to Tb3+ were studied and they are proved to be dipole-dipole and dipole-quadrupole mechanism, respectively. Furthermore, by changing the relative doping concentration ratio of Ce3+/Eu2+ and Ce3+/Tb3+, the phosphors Ca2Mg0.25Al1.5Si1.25O7:Ce3+,Eu2+/Tb3+ can emit blue-green color light, demonstrating that the phosphors are promising blue-to-green emitting phosphors for application in phosphor-converted white light emitting diodes.3. A series of three color and white phosphors Ca2Mg0.75Al0.5Si1.75O7:Ln(Ln=Ce3+, Dy3+, Eu3+, Sm3+) were synthesized. The luminescent properties, color coordinates and their applications in light emitting diodes devices of these phosphors were studied. The blue, red and white light emitting diodes devices are packaged by the combination of the prepared phosphors with the ultraviolet chip. The luminous efficiency, CIE chromaticity coordinates, color temperature and color rendering index of the devices were tested, showing that these phosphors can be applied in white light emitting diodes.4. Single-phase white-emitting phosphor Ca20Al26Mg3Si3O68:Ce3+,Dy3+ were prepared by high temperature solid state method, and their luminescent properties were also investigated. There are two emission peaks peaking at 407 and 577 nm in the emission spectra, which are attributed to the electronic transitions of Ce3+ and Dy3+, respectively. More importantly, the existence of effective energy transfer from Ce3+ to Dy3+ is demonstrated by excitation and emission spectra and fluorescence lifetime. Finally, by changing the relative doping concentration ratio of Ce3+/Dy3+, the phosphor can realize the emitting of blue-white, this indicating that the phosphor has potential application value in white light emitting diodes. Yellow-red multicolor-emitting phosphors Ca20Al26Mg3Si3O68:Dy3+,Eu3+ were also synthesized. The phosphors Ca20Al26Mg3Si3O68:Dy3+ and Ca20Al26Mg3Si3O68:Eu3+ were mearsured X-ray photoelectron spectroscopy and the site-selective spectroscopy, respectively to confirm the doping position of Dy3+ and Eu3+. Then, the effective energy transfer from Dy3+ to Eu3+ ions has been confirmed and investigated. The results indicate that the phosphors are promising single-phase yellow-red phosphors.5. Ln(Ln=Ce3+, Tb3+, Eu3+) ions-doping Ca2Mg0.5Al Si1.5O7, Ca2Mg0.25Al1.5Si1.25O7, Ca2Mg0.75Al0.5Si1.75O7 and Ca20Al26Mg3Si3O68 tricolor emission phosphors are synthesized, respectively. The crystal phase, luminescent properties and the application in ultraviolet white light emitting diode of these phosphors are investigated. By comparison among these tricolor emission phosphors, the best tricolor emission phosphors were selected, then a series of white light emitting diode prototypes are fabricated by combining near- ultraviolet light emitting diode chip and the selected best tricolor phosphors with various ratios in weight. The results demonstrate that these phosphors show potential application in ultraviolet white light emitting diode.