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Study on Eu or Tb Doped Alkaline Earth Polysilicate Phosphors

Author: JiaoFangFang
Tutor: DiYongQing
School: Hebei University
Course: Applied Chemistry
Keywords: Alkaline earth polysilicate gel-combustion method luminescence long afterglow doping
CLC: O613.72
Type: Master's thesis
Year: 2009
Downloads: 81
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In the recent years, silicates phosphors are attracted more and more attention because of its good chemical stability, strong water resistance, light-emitting color variety and extensive applications.At present, the traditional method to synthesize silicate-host luminescence materials is solid-state reaction. But this process has a lot of disadvantages, such as the synthesis temperature is high, the reaction time is long, the partical size is large, and the hardness of the powder is strong, it need grounding to reduce the particle size, which results in the decrease of luminescent brightness and afterglow. So this method is restricted for further development. Therefore, exploring new synthesis method is gradually eyed by more and more people.Gel-combustion method is a new soft-chemical process combined with ion homogeneous distribution of sol-gel method and high efficiency of combustion method. Compared with traditional solid state reaction, gel-combustion method has many advantages, such as uniform composition, short calcination time, simple operation, and small particles, and so on. It provides a new idea for saving energy and lowering energy consumption.In our pesent work, a series of alkaline earth polysilicate phosphors doped with rare earth ions were successfully synthesized by gel-combustion method. The as-synthesized phosphors were investigated by X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and Fluorescence spectrophotometer. According to that, we get some valuable conclusions as follows:1. Blue-purple emitting material CaMgSi2O6:Eu2+ with high brightness was synthesized by gel-combustion method in weak reductive environment. The as-synthesized CaMgSi2O6:Eu2+ has monoclinic crystal structure. When the calcination temperature is 1000℃, the initial particles are nearly spherical in shape, and the mean size is about 300nm. The particle size increases with the increase of the calcination temperature. Spectral analysis indicates that this phosphor has a broad band emission peak at 450 nm, this peak was made by the transition 4f65d1→4f7 of Eu2+, which was caused by the [EuO6] emitting center formed in CaMgSi2O6 host. Moreover, the effects of different concentration of doped Eu2+ and reductive temperature on the luminescent property were investigated.2. On the basis of the synthesis of a novel host SrMgSi2O6 by gel-combustion method, the effects of co-doped Eu2+ and Ln3+(Ln=La, Ce, Nd, Sm, Gd, Dy) on the crystal structure and luminescent properties were investigated in detial. It is found that SrMgSi2O6:Eu2+,Ln3+ phosphors have akermanite structure and belong to tetragonal crystal structure. The shape and position of peaks in emission spectrums have almost no change with the variation of co-doped Ln3+. The emission spectrums are all broad band continuous spectrums and the main peak is at 470nm. The series of samples show long afterglow properties. But the kind of doped auxiliary activators has great effects on the luminescent intensity and the long afterglow properties of the materials. The approximate order of long afterglow intensity are as folows:Dy3+> Nd3+> Eu2+> La3+> Gd3+> Ce3+> Sm3+. Among them, Dy3+ is best on. The persistence time of Sr0.94MgSi2O6:Eu2+0.02, Dy3+0.04 is the longest, about 4h. Moreover, the effects of the concentration of Eu2+ and Dy3+, the reductive temperature and the dosage of H3BO3 on luminescent intensity were discussed. Also, the long afterglow luminescence mechanism of SrMgSi2O6:Eu2+,Ln3+ was explained.3. A novel yellow emitting material SrMgSi2O6:Tb3+ was synthesized by gel-combustion method in weak reductive environment. The as-synthesized SrMgSi2O6:Tb3+ phosphors possess the similar tetragonal crystal structure. When the calcination temperature is 1100℃, the initial particles are nearly spherical in shape, and the mean size is about 240nm.The emission spectrum is composed of a series of sharp peaks, located respectively at 473nm, 491nm,547nm,585nm. These emission peaks are ascribed respectively to Tb3+ ions transition of 5D3→7F3,5D4→7F6,5D4→7F5,5D4→7F5 in SrMgSi2O6 host. The emission peak at 547nm,491nm and 473nm are all strong, the samples show yellow emitting under UV irradiation. Moreover, it is found that the concentration of doped Tb3+ and reductive temperature have great significant effect on the luminescent property of the phosphors.4. The persistent phosphor Sr3MgSi2O8:Eu2+,Dy3+ with orthorhombic system was successfully synthesized by gel-combustion method. Its emission spectrum is a broad band with the peak at about 460nm due to the typical transition of 4f65d1→4f7 from Eu2+; the excitation spectrum is also a broad band with a main peak at about 414nm and the secondary at about 400nm. Compared with Sr2.94MgSi2O8:Eu2+0.02,Dy3+0.04 synthesized by high temperature solid-state reaction, excitation spectrumof as-synthesized sample shift to long wavelength. Moreover, the effects of reductive temperature, reductive time, the mol fraction of H3BO3 and the dosage of urea on the luminescent property were investigated.5. A series of new red-emitting polysilicate phosphors Sr2MgSi2O7:Eu3+ and Sr3MgSi2O8:Eu3+ were successfully synthesized by gel-combustion method. It is found that doped Eu3+ has little effect the structure of the host. The excitation spectra of the samples show a broad band between 220nm and 350nm, which is ascribed to the charge transference from O2- to Eu3+. The sharp peaks after 350nm are due to the f-f transition from Eu3+, of which the strongest one is located at 400nm. The excitation spectrum is composed of two strong emission peaks located at 592nm and 618nm respectively, which are attributed to the transition 5D0→7F1 and 5D0→7F2 of Eu3+ respectively. Besides, the effects of different concentration of doped Eu3+ on the luminescent intensity were investigated. It is interesting that the concentration quenching can not be found in the samples of Sr2-xMgSi2O7:Eu3+x, and their red-emitting is very bright. Among the samples of Sr3-xMgSi2O8:Eu3+x, the concentration quenching occurs when the concentration of Eu3+ is 8%.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Non-metallic elements and their compounds > Part Ⅳ family of non-metallic elements (carbon and silicon ) and its compounds > Si Si
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