Eu3+ doped yttrium orthosilicate (Y2SiO5) phosphor was prepared by the sol-combustion method using citric acid as
complexing agent in this experiment. The X-ray diffraction (XRD) pattern, excitation and emission spectra were used to
investigate the crystal structure and luminescent properties of the phosphor. XRD pattern showed that pure Y2SiO5:Eu3+
phosphor was obtained. The excitation spectrum was composed of a broad band from 200-350 nm and a series of narrow
bands from 350-500 nm, in which the excitation peaks at 400 nm and 470 nm were stronger. The emission spectrum
showed the most intense emission peak was located at 613 nm, which corresponded to the 5D0→7F2 transition of Eu3+.
The results showed that this phosphor could be excited by UV or blue light and emit red light. The luminescent intensity
depends on the concentration of Eu3+ and it reached the maximum when the molar concentration of Eu3+ was 4 mol%. In
this study, we found that the emission intensity reached maximum when the ratio of citric acid and Y3+ was 1.5:1. The
results indicated that Y2SiO5:Eu3+ is a potential red-emitting candidate phosphor for white light-emitting diodes.
The Y2Si2O7:Tb3+ phosphor was synthesized by high temperature solid state method. The crystal structure and
luminescent properties of phosphors were studied by XRD pattern, excitation and emission spectra in this paper. XRD
pattern showed that the sample was single phase Y2Si2O7 crystal and the crystal lattice constants a=0.806nm, b=0.934
nm, and c=0.692 nm. The excitation spectrum is composed of a broad band centered 290nm and three narrow bands
corresponding to 4 - 4 transition of Tb3+ centered 378 nm, 400nm and 420nm, respectively. The emission peaks of
phosphor were located at 487nm, 546nm, 584nm and 623nm, which were corresponding to 5D4-7F6, 5D4-7F5, 5D4-7F4 and
5D4-7F3, respectively. The influences of Tb3+ concentration on the luminescent intensity of Y2Si2O7:Tb3+ phosphor was
studied. The results indicated that this phosphor could act as a candidate green phosphor for UV-excited white LED.
The red long afterglow phosphor CaTiO3 activated with Pr3+ was formed by wet-dry method in this study. The luminescent properties of this sample had been studied systematically. The X-ray diffraction (XRD) patterns of the powder reveal that CaTiO3:Pr phase was obtained by wet-dry process. The afterglow decay curves were measured and the afterglow time was over 40 minutes. The excitation spectra and emission spectra were measured. The emission peak was at 613nm, due to the transition of 1D2-3H4. With the function of weak crystal field the main emission divided into
612nm and 614nm. In spite of the main emission peak, phosphor had a shoulder emission peak at 620-628nm. Changes of Pr3+ molar ratio had little effect on the emission spectra, but with Pr3+ 0.2%, phosphor had an emission peak at 626nm. The excitation peak was at 342nm, with a shoulder peak at 400nm. Compared with SS, this less time and less energy was used and the same result is obtained.
The red phosphors of Y2O2S:Eu3+ were synthesized by combustion reactions from mixed metal nitrate reactants and a fuel CH4N2S with ignition temperatures of 450°C. Sulfur was produced by CH4N2S decomposed at high temperature.
Y2O3 decomposed by Y(NO3) 3 reacted in Sulfur atmosphere to synthesize Y2O2S host. From altering the ratio of CH4N2S and metal nitrate, the pure phase Y2O2S:Eu3+ red phosphor was obtained. The conclusion was proved by XRD patterns and emission spectrum.
Powder phosphors of yttrium aluminum garnet Y3Al5O12 (YAG), activated with trivalent cerium (Ce3+) was synthesized
by combustion from mixed metal nitrate reactants and urea with ignition temperature of 500C°~550C°. Sintering the
precursor can improve the crystallization of YAG: Ce3+ phosphors so to promote the luminescence intensity. The
influence of the concentration of Ce 3+ on the luminescence character was studied. The crystalline structure and
morphology are observed by x-ray powder diffraction picture and SEM picture respectively.
CaO-MgO-B2O3-SiO2 glass co-doped with Eu2+, Dy3+ was prepared, which showed the Long lasting phosphorescence. The luminescent properties of this photoluminescence glass had been studied systematically. The main emission peaking at 476nm was ascribed to the 4f5d→4f transition of Eu2+ in glass matrix. The optical absorption spectra of the samples fabricated under the ambient and reducing atmospheres were measured separately. The sample fabricated in the ambient atmospheres was transparent in wavelength region from 340nm to 1μm. While the samples fabricated in the reducing atmosphere a strong absorption band was observed from 350 to 450nm, and the peak was at the 375nm. This band could be assigned to the absorption of Eu2+ ions. The excitation spectra of the sample fabricated in the reducing atmosphere was measured. A strong peak at 396nm and a weak peak at 439nm were observed. They were ascribed to the transitions of Eu2+ ions. The results were conformed to the conclusion of the absorption spectrum. The afterglow decay process could be divided into two stages. One is an instant attenuation, and the other is a slow. Incorporation of rare ions Eu2+ and Dy3+ into glass matrix could largely change the long afterglow properties of the glass. The analytical results indicated that the co-doped Dy3+ ions acted as hole-trap levels and captured the free holes. It resulted in the property of long lasting phosphorescence of CaO-MgO-B2O3-SiO2 glass co-doped with Eu2+, Dy3+.
Eu2+, Nd3+ co-doped calcium aluminate (CaAl2O4) phosphor with high brightness and long afterglow were fabricated by urea-nitrate solution combustion synthesis at 600°C. The phosphor powder of combustion synthesis were generally more homogeneous and had fewer impurity than phosphor fabricated by conventional solid-state methods, the character could conduce to obtain more exact data. The excitation and emission spectrum indicated that there waxs only one luminescence center Eu2+, both of the characteristic spectrums of Eu3+ and Nd3+ weren't discovered. As a secondary activator, Nd3+ could make remarkable influence on the afterglow of phosphor. From altering the moral ratio of Eu2+ and Nd3+, the lasting time of afterglow and thermoluminescence were studied respectively, when Nd3+ wasn't appended, the intensity of initial brightness could compared with other materials which had different ratio of Eu2+ and Nd3+, however the brightness of afterglow decayed rapidly, the lasting time and brightness of afterglow were improved with reduce the radio of Eu2+ and Nd3+, while the ratio achieved some value, the lasting time of afterglow become shorten with the reduce of ratio of Eu2+ and Nd3+. Moreover the depth of trap was calculated from the parameter of thermoluminescence. However, the emission spectrum and XRD patterns didn't change obviously with the altering ratio of Eu2+ and Nd3+. It showed that the little amount of doped rear earth ions (Eu2+ and Nd3+) had almost no effect on the CaAl2O4 phase composition. Based on these conclusions, the model of the luminescence process of CaAl2O4:Eu2+, Nd3+ was built.
SrAl2O4:Eu2+,Dy3+ was synthesized from various composition by high-temperature solid-state reaction and the effect of composition on the afterglow phosphorescence have been evaluated. The luminescent propertis were depended to a large extent on the calcination conditison and stoichiometry under which the phosphor is prepared. In order to study the luminscent character of the long-afterglow material, the whole decay curves of 10h were measured. The emission spectra and the excitation spectra of SrAl2O4:Eu3+,Dy3+ powders were shown, and the poweder x-ray diffraction pattern was obtained also.
By changing the ratio of Al:Sr, we get a new type phosphor SeAl3O5(OH):Eu2+,Dy3+ emitting blue light with the afterglow characteristics of over 10 hours. The emitting peak is at 484nm, which is corresponding to the spectral transition 4f5d of Eu2+. The influence of different temperatures and different fluex on the luminescent properties of SrAl3O5(OH):Eu2+,Dy3+ was studied. The results indicate that increasing the sintering temperature helps crystal to grow, and that the luminescent properties of SrAl3O5(OH):Eu2+,Dy3+ is improved by higher temperature or the flux especially H3BO3, which increases the initial brightness and prolongs the afterglow time comparing with the SrAl3O5(OH):Eu2+,Dy3+ that without additives.
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