Study on Luminescence Properties and Energy Transfer of SrCaSiO_4∶Eu~(2+),Ce~(3+) Phosphor
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SrCaSiO4:Eu2+,Ce3+ has been prepared through high-temperature solid state reaction,and the spectrum and lifetime decay curves has been tested.The phosphors can match UV LED,and emit a broad band with a maximum at 500 nm.In SrCaSiO4:Ce3+,Eu2+ phosphors,energy transfer could been found between Ce3+ and Eu2+.In the fluorescent powder SrCaSiO4:Eu2+,the doping Ce3+ will make Eu2+ decay lifetime increase,and make Ce3+ decay lifetime become short,it also proves that there exist energy transfer.Cite
Due to a lot of advantages, such as energy saving, high efficiency and long lifetime, white light emitting diode (W-LED) has been widely applied in many areas. The common way to fabricate W-LED is by painting a yellow-emitting phosphor on the blue LED chip. Since blue LED emits from 430 nm to 480 nm, the absorption energy for a better yellow-emitting phosphor should match that spectral region of LED emission. YAG∶Ce3+ shows a strong broad band absorption around 465 nm and emits at about 540 nm; therefore it has been used as the main yellow-emitting phosphor in W-LED. However, the weakness of W-LED composed of blue LED and YAG∶Ce3+ is the shortage of its red-emission component. To overcome this weakness, one of the following approaches could be chosen: 1.Adding some red-emitting components into YAG∶Ce3+ phosphor; 2.Doping other cations in YAG∶Ce3+ lattice. Lanthanide ions are the appropriate ones for this doping YAG∶Ce3+ since their ionic radii are very close to that of Y3+ ion. Many papers have reported the study on lanthanide doping. In this paper, the doping effects of Pr3+ and Sm3+ on the luminescence properties and fluorescence lifetime of YAG∶Ce were systematically studied in order to understand the rule. Phosphors were synthesized by high-temperature solid-state reaction under reducing atmosphere. The X-ray diffraction patterns presented Pr3+ and Sm3+ can partially replace Y3+ and the lattice phases do not change. The doping effects of Pr3+ and Sm3+ on the luminescence properties and fluorescence lifetimes of (Y0.96-xLnxCe0.04)3Al5O12 (Ln= Pr3+,Sm3+) were studied. The emission and excitation spectra of the samples are recorded. In the (Y0.96-xPrxCe0.04)3Al5O12 system the emission band of Pr3+ was at about 609 nm; and in the (Y0.96-xSmxCe0.04)3Al5O12 system the emission band of Sm3+ was at about 616 nm. So it can increase the color rendering index (CRI) of YAG∶Ce phosphors doped by Pr3+ or Sm3+. Fluorescence lifetimes of the Ce3+ in (Y0.95Pr0.01Ce0.04)3Al5O12, (Y0.95Sm0.01Ce0.04)3Al5O12, (Y0.96Ce0.04)3Al5O12 are measured. The lifetime decreased due to the doping of Pr3+or Sm3+ in YAG∶Ce3+.
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There exists an increasing demand for red emitting phosphors to be used in color display and illumination.SrAl12O19∶Eu2+ has attracted much attention for its excellent properties such as high quantum efficiency and good stability.However,the emission of SrAl12O19∶Eu2+ peaks at 400 nm,which is hard to be used in display and illumination.As we know,Cr3+ with red emission lines is one of the most used activators for solid state laser and other luminescent materials.Therefore,we have studied the emission and excitation spectra as well as energy transfer in SrAl12O19∶Eu2+,Cr3+.The Cr3+,Eu2+ singly doped and co-doped samples were synthesized by solid-state reaction at 1 400 ℃.The emission band of Eu2+ peaked at 400 nm is originating from the 5d-4f transition,which has large spectral overlaps with the 4A2→4T1 Absorption band of Cr3+ covering between 350 nm and 450 nm in the ultraviolet-blue region.It means the possibility of energy transfer from Eu2+ to Cr3+.The conversion of violet-blue emission to the red may be obtained by the energy transfer.In the co-doped samples,the emission band of Eu2+ appears in the range of excitation spectra of Cr3+ emission,which indicates the occurrence of energy transfer from Eu2+ to Cr3+.In order to explain energy transfer further,the lifetime of Eu2+ emission in SrAl12O19∶1%Eu2+,x%Cr3+(x=0,0.2,1.0,2.0,3.0,4.0,5.0) has been measured.It shows that the lifetime of Eu2+ reduces following increasing Cr3+ concentration due to the energy transfer from Eu2+ to Cr3+.The energy transfer efficiency as a function of Cr3+ concentration has been calculated using the measured fluorescent lifetimes of Eu2+,indicating the transfer efficiency increases with increasing Cr3+ concentration,and may reach 50% as Cr3+ concentration is 0.05.
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An orange-emitting phosphor was obtained via efficient Ce3+–Mn2+ and Eu2+–Mn2+ energy transfers in La9.33(SiO4)6O2, and has been developed for solid state UV/near-UV white lighting applications. The luminescence properties and energy transfer from Ce3+ to Mn2+ and Eu2+ to Mn2+ are investigated. The La9.33(SiO4)6O2:Ce3+, Mn2+ phosphor shows a blue emission centered at 380 and an orange emission peaking at 590 nm, which could be ascribed to the allowed 5d → 4f transition of the Ce3+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. Upon excitation at 365 nm, the Eu2+, Mn2+ co-doped La9.33(SiO4)6O2 phosphor exhibits the Eu2+ green emission band and the Mn2+ orange emission band. Non-radiative transitions between the Ce3+/Eu2+ and Mn2+ ions in the La9.33(SiO4)6O2 host are both demonstrated to be attributable to dipole–quadrupole interactions. The intensity ratio of the Mn2+ emission bands can be enhanced through the increase of the Mn2+ content, which is attributed to the efficient energy transfer from Ce3+/Eu2+ to Mn2+, and the corresponding chromaticity coordinates (0.50, 0.38), (0.51, 0.46) were obtained with the La9.33(SiO4)6O2:Ce3+, Mn2+ and La9.33(SiO4)6O2:Eu2+, Mn2+ samples. Results indicated that the as-prepared phosphors might have promising applications in white-light LEDs as an orange-emitting phosphor.
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Europium
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Phosphor SrGdGa3O7:Eu3+ has been synthesized by solid-state reaction at high temperature.The bands of ff transfer of Eu3+ and 8S7/26I7/2 transfer of Gd3+ appear in the exicitation spectrum,which is consistent with diffuse reflectance spectrum.When monitored by 613 nm,there are 8S7/2-6I7/2 and 8S7/2-6P7/2 transitions of Gd3+,indicating that the energy transfer from Gd3+ to Eu3+ happens.Emission spectrum is dominated by the main lines at 613 nm due to the 5D0-7F2 transition,indicating Eu3+ occupies Gd site(Cs)without inversion symmetry.The splitted energy levels of 7F1 and 7F2 have been calculated by emission spectrum at 12 K.Emission intensity of Eu3+ decreases gradually with temperature increasing,and the resolution of emission peak also decreases.Decay curves of Eu3+(5D0→7F2) at different temperature are similar and emission intensity decrease with temperature increasing.The lifetime of Eu3+ is in the order of millisecond,which is reasonable for the forbidden transfer(5D0→7F2).
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A series of Eu2+- and Mn2+-coactivated CaAl2Si2O8 phosphors have been synthesized at 1400 °C under a reduced atmosphere and their luminescence properties have been investigated as a function of activator and coactivator concentrations. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the systematic relative decline and growth of emission bands of Eu2+ and Mn2+, respectively. The critical distance and average separation of Eu2+ and Mn2+ have also been calculated. By utilizing the principle of energy transfer, we have also demonstrated that with appropriate tuning of activator content CaAl2Si2O8:Eu2+,Mn2+ phosphors exhibit great potential to act as a phosphor for white-light ultraviolet light-emitting diodes (UVLEDs).
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A series of new phosphors of were synthesized by conventional solid-state reactions. The X-ray diffraction data indicate that a pure phase of can be successfully obtained. The photoluminescence (PL) spectra, quantum efficiency, and CIE coordinates of were investigated. The PL and PL excitation spectra indicate that the emission wavelengths of are 372 and 398 nm (with full width at half maximum of 33 nm) attributed to the – transition of the activator, respectively. displays green emission at 483, 543, 584, and 620 nm, while shows a dominating emission peak at 621 nm, which is attributed to the transition. The quantum efficiencies of optimized , , and were found to be 43, 21, and 19%, respectively. The phosphors may provide a new kind of luminescent material under UV excitation.
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ABSTRACT Sr 3 MgSi 2 O 8 :Ce 3+ , Dy 3+ phosphors were prepared by a solid‐state reaction technique and the photoluminescence properties were investigated. The emission spectra show not only a band due to Ce 3+ ions (403 nm) but also as a band due to Dy 3+ ions (480, 575 nm) (UV light excitation). The photoluminescence properties reveal that effective energy transfer occurs in Ce 3+ /Dy 3+ co‐doped Sr 3 MgSi 2 O 8 phosphors, and the co‐doping of Ce 3+ could enhance the emission intensity of Dy 3+ to a certain extent by transferring its energy to Dy 3+ . The Ce 3+ /Dy 3+ energy transfer was investigated by emission/excitation spectra, and photoluminescence decay behaviors. In Sr 2.94 MgSi 2 O 8 :0.01Ce 3+ , 0.05Dy 3+ phosphors, the fluorescence lifetime of Dy 3+ (from 3.35 to 27.59 ns) is increased whereas that of Ce 3+ is greatly decreased (from 43.59 to 13.55 ns), and this provides indirect evidence of the Ce 3+ to Dy 3+ energy transfer. The varied emitted color of Sr 3 MgSi 2 O 8 :Ce 3+ , Dy 3+ phosphors from blue to white were achieved by altering the concentration ratio of Ce 3+ and Dy 3+ . These results indicate Sr 3 MgSi 2 O 8 :Ce 3+ , Dy 3+ may be as a candidate phosphor for white light‐emitting diodes. Copyright © 2012 John Wiley & Sons, Ltd.
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Abstract Tb 3+ ‐doped and Eu 2+ , Tb 3+ co‐doped Ca 9 Y( PO 4 ) 7 phosphors were synthesized by conventional solid‐state method. Additionally, the luminescence properties, decay behavior and energy transfer mechanism have already been investigated in detail. The green emission intensity of Tb 3+ ions under NUV excitation is weak due to its spin‐forbidden f‐f transition. While Eu 2+ can efficiently absorb NUV light and yield broad blue emission, most of which can be absorbed by Tb 3+ ions. Thus, the emission color can be easily tuned from cyan to green through the energy transfer of Eu 2+ →Tb 3+ in Ca 9 Y( PO 4 ) 7 :Eu 2+ ,Tb 3+ phosphor. In this work, the phenomenon of cross‐relaxation between 5 D 3 and 5 D 4 are also mentioned. The energy transfer is confirmed to be resulted from a quadrupole‐quadrupole mechanism.
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