Preparation And Photoluminescence Properties Of Y₂SiO₅ And Sr₂SiO₄ Phosphors

The w-LED is considered as an environmental friendly lighting due to its advantages such as high lighting efficiency, pollution-free and long lifetime. The ideal of white light could be prepared by using the effective combination of phosphors and LED chips, therefore the fluorescent light powder performance is good or bad, which will influence directly on the color effect of white LED. Solar cells can be used in the communications/electricity, petroleum, marine, and many other areas as the pollution-free renewable solar energy because it can convert the solar energy into electrical energy. But the solar cell does not match with the solar spectrum, leading to the low efficiency for the light conversion. Therefore, looking for the right down-conversion luminescence materials is of great significance, in which the ultraviolet (UV) wavelengths unabsorbed by solar cells can be converted into the visible-near infrared (NIR) wave band.In this paper, Ce3+-doped and Bi3+-Eu3+ co-doped Y2SiO5 phosphors which have potential to be used for LED were synthesized by solid-state reaction method respectively. Ce3+-Tb3+-Yb3+tri-doped Sr2Si04 down-conversion material for Si solar cells were also studied.The thesis consists of the following results:1. The single phase X2-Y2Si05:Ce3+ phosphors were prepared by the solid-state method at high temperatures. The excitation spectra is a band spectrum of 280-370nm, and the emission peaks are located at 393nm and 418nm peaks, corresponding to 5d?4f spin allowed transition. With adding flux of B2O3, NaF and BaO, the luminescence intensity of specimens have been changed dramatically. The intensity can be enhanced to 1.8 times and 1.4 times respectively in the condition of 1wt%Ba2+ and 1wt%Na+.2. The Y2Si05:Bi3+, Eu3+ phosphors were prepared. Single Bi3+-doped Y2SiO5 exhibited three discernible emission peaks at-358,-408, and ?490 nm, respectively, upon UV excitation. When Eu3+ is codoped into Y2Si05:Bi3+, a red emission peaks at 612nm appeared, which is attribute to 5D0?7F2 of Eu3+ By adjusting the doping ratio of Bi3+/Eu3+, tunable emissions of phosphors between blue and red can be objected. Y2Si05:Bi3+, Eu3+ is a promising candidate of white light emitting.3. The luminescent properties of Sr2Si04:Ce3+, Tb3+, Yb3+ were studied. Single Yb3+-doped Y2Si05 exhibited a emission peak at 977 nm which is close to the band gap of Si solar cell. The near-infrared emission intensity was remarkably enhanced by adding Ce3+ and Tb3+ as sensitized ions. The Ce3+can transfer energy to Tb3+ ions by means of dipole-dipole interactions. Cooperative energy transfer occurred between Tb3+and Yb3+.The optimum doping concentration was obtained to be 4mol% Ce2+,6mol% Tb3+ and 3mol%Yb3+.