Structures And Photoluminescence Properties Of Polymer-Derived Silicon Oxynitride White Emitting Phosphors

Compared with traditional light sources,white light-emitting diodes(w-LEDs)are considered to be the most promising and hopeful next-generation green light source.The single-matrixed white phosphors have attracted much attention due to their significant application potential in w-LEDs.Since the silicon oxynitride phosphor has stable thermochemical properties,excellent luminescent properties and stable structures,the preparation of Eu-activated and Eu/Ce-coactivated silicon oxynitride phosphors by employing the polymer-derived method with polycarbosilane,Eu acetylacetonate,and Ce acetylacetonate as starting materials is investigated in this work.The effects of different polycarbosilanes and the atomic ratios of Si:Eu(Si:Eu:Ce)on the chemical compositions,phase structures,morphologies and luminescence properties of the silicon oxynitride phosphors were systematically studied.The phase structures of the Eu-activated and Eu/Ce-coactivated silicon oxynitride white emitting phosphors were analyzed,and the possible luminescence mechanisms for the Eu-activated and Eu/Ce-coactivated silicon oxynitride white emitting phosphors were discussed.The experimental results revealed that the dominate phase in the Eu-activated silicon oxynitride phosphors sintered at 1650 0C was the ?-Si3N4-like phase.As the initial atomic ratio of Si:Eu changed gradually from 32:0,1 to 32:1,the emission color of the Eu-activated phosphor was tunable from blue to white and finally to yellow.The CIE coordinate for the phosphor with the initial atomic ratio of Si:Eu being 32:0.59 under the near-UV(355 nm)excitation was(0.35,0.32),which is close to(0.33,0.33)for the standard white light.The dominate phase for the Eu/Ce-coactivated silicon oxynitride phosphors sintered at 1650 0C was alsol the ?-Si3N4-like phase.Doping Ce in Eu-activated phosphors improved the white light quality and luminescence intensity.The CIE coordinate for the phosphor with the initial atomic ratio of Si:Eu:Ce being 32:0.45:0.2 under the near-UV(340 nm)excitation reached(0.33,0.33).The luminescence intensity was about 1 times higher than that of the phosphor with the initial Si:Eu:Ce being 32:0.45:0.It was found that the dominated ?-Si3N4 phase in the Eu-activated and Eu/Ce-coactivated silicon oxynitride phosphors consisted of two space groups P63 and P63/mW.Eu ions and Ce ions located at interstitial sites with a larger channel surrounded by six-ring Si(N/O)4 tetrahedrons.Eu ions were coordinated by nine N/O atoms and Ce ions were coordinated by either nine or six N/O atoms.The emission peaks at the low and high energy levels for the Eu-activated white emitting sample could be attributed to the luminescence centers of Eu2+ions in P63/m and P63,respectively.Similarly,the emission peak at the low energy level for the Eu/Ce-coactivated white emitting sample might be attributed to P63/m:Eu,and that at the high energy level to joint action of P63:Eu,P63/m:Ce and P63:Ce.