Preparation And Luminescence Properties Of Alkaline Earth Composite Silicate Phosphors For White-led

White light emitting diodes (LED) have attracted widespread interest due to their little volume, energy-saving, high efficiency, mercury pollution-free, long service life and so on, so it is honored to the fourth generation illuminating sources. The most mature method for achieving White LED is phosphor conversion. Therefore, more and more attention has been paid to the preparation and the properties of the phosphors for White LED.Alkaline earth polysilicate phosphors have more advantages on chemical stability, heat stability, excellent water resistance, varied luminescence color and wide application, so more attention is focused on this kind of phosphors.So in our present work, a series of alkaline earth polysilicate phosphors doped with rare earth ions for White LED were successfully synthesized by gel-combustion method. The as-synthesized phosphors were investigated by X-ray diffraction analysis (XRD), Energy Dispersive Spectrometer (EDS), Scanning Electron Microscope (SEM) and Fluorescence spectrophotometer. According to that, we get some valuable conclusions as follows:1. Eu2+ doped novel alkaline earth polysilicate blue emitting phosphors Sr2MgSi3O9:Eu2+ were synthesized by gel-combustion method. The phosphors possess the tetragonal crystal structure. The initial particles of the phosphors are nearly spherical in shape, and the grain size is about 100nm in diameter. The excitation spectrum of Sr2MgSi3O9:Eu 2+ is a broad band in the range of 250~450nm,the main peak is at 424nm and the secondary peak is at 400nm. So, the phosphors can be excited efficiently by UVLED chip with the near-UV radiation of 360~400 nm. The emission spectrum is also a broad band, and the emission peak is at about 470nm which is ascribed to Eu2+ ions typical transition from 4f5d to 4f. Sr2MgSi3O9:Eu2 + shows good prospect for blue phosphors of white LED. Moreover, the effects of the doping concentration of Eu2+, the sintering temperature and the co-doped ions on the luminescence properties of the phosphors have been discussed.2. Ce3+, Tb3+ co-doped novel phosphors Sr2MgSi3O9:Tb3+,Ce3+ were synthesized by gel-combustion method. Sr2MgSi3O9:Tb3+ and Sr2MgSi3O9:Tb3+,Ce3+ phosphors possess the similar tetragonal crystal structure as that of Sr2MgSi2O7. The initial particles of as-synthesized phosphors are nearly spherical in shape, and the particle size is about 100nm in diameter. The excitation spectrum of Sr2MgSi3O9:Tb3+ is a broad band and the main peak is at 249nm. The emission spectrum is composed of a series of peaks, located respectively at 473nm, 491nm, 547nm and 585nm. The main peak is at 473nm (5D3→7F3), and the secondary peak is at 547nm (5D4→7F5). The excitation spectrum of Sr1.955MgSi3O9:Tb3+0.04, Ce3+0.005 displays two broad bands with two peaks around 249nm and 335nm respectively; the latter peak is much stronger than the former. Under 335nm irradiation, the emission spectrum is composed of two parts. One part is a broad band at around 400nm, which belongs to the emission of Ce3+. The other part is composed of a series of peaks, located respectively at 491nm, 547nm and 588nm. These emission peaks are ascribed respectively to Tb3+ ions transition of 5D4→7FJ (J = 6, 5, 4) in Sr2MgSi3O9:Tb3+,Ce3+. The main emission peak is at 547nm (5D4→7F5). Moreover, the effect of Ce3+ doping amount on luminescent intensity was discussed. It is found that energy transfer from Ce3+ to Tb 3+ is efficient and sensitization lie in Ce3+ to Tb3+ in Sr2MgSi3O9 host under UV light.3. Eu3+ doped novel alkaline earth polysilicate red phosphors xSrO·MgO·ySiO2(x = 1~2,y = 2~3) were synthesized by gel-combustion method. The as-synthesized phosphors possess the similar tetragonal crystal structure as that of Sr2MgSi2O7. The excitation spectrum of samples presents wide band absorption between 220~300nm, which is ascribed to the charge transfer between Eu3+-O2-. The sharp peaks after 300nm belong to f-f transition of Eu3+, and the strongest sharp peak is located at 400nm. Therefore, samples can be efficiently excited by ultraviolet radiation from InGaN chip. The emission spectrum consists of two strong emission peaks at 592nm and 618nm, which are ascribed to 5D0→7F1 and 5D0→7F2 respectively. Moreover, the effect of the doping concentration of Eu3+, co-dope Gd3+ , Ti4+ and charge compensation agent Li+, Na+ and K+ on luminescent properties were discussed.4. Eu2+ doped the series of Sr4Si3O8Cl4:Eu2+ blue-green phosphors were synthesized by gel-combustion method. The as-synthesized phosphors have the same orthorhombic crystal structure as that of Sr4Si3O8Cl4. The excitation spectrum of Sr4Si3O8Cl4:Eu2+ is a broad band in the range of 250~400nm, and the main peak at 324nm, which can be excited efficiently by UV and NUV radiation generated by UVLED chip. Under the radiation of 324nm, the emission spectrum is also a broad band with the main emission peak at about 484nm. It's ascribed to Eu2+ ions typical transition from 4f5d to 4f. Sr4Si3O8Cl4:Eu2+ shows good prospect for blue-green phosphors of white LED. It is found that doping Mg2+ ion in host leads to blue shift of the emission spectrum of Sr4-xMgxSi3O8Cl4: Eu2+. The reason is that doping Mg2+ ions change the crystal field of Eu2+. The main emission peak shifts from 484nm to 436nm when the concentration of Mg2+ changes from 0 to 2.0, the emitting colour varies from blue-green to blue; the main excitation peak shifts from 324nm to 343nm, so stokes shifts decrease, and luminous efficiency is improved. Moreover, it is found that the luminescent intensity increases with the increase of the concentration of Mg2+ when the concentration of Mg2+ is excess to 0.5, and blue emitting becomes strong.