Synthesis And Property Of Polymer Phosphors In White Light Emitting Diode (WLED)

Following the incandescent lamp, fluorescent lamp and high pressure gas discharge lights, white-light LED with small power consumption, long life, environmental protection and other advantages, is considered as a new generation light source. According to the theory of chromaticity, the white light can be obtained by mixing blue and yellow light. The sensitized Dy(III) ion with the special structure can emit blue light at about480nm and yellow light at about572nm. If the blue/yellow intensity ratio can be tuned properly, a white light would be obtained. In this paper, the dysprosium polymer phosphor was prepared by the technological means from coordination to polymerization and can emit nearly white yellowish with excitation at the wavelength of365nm. Then the blue phosphor zinc polymer was obtained by free radical polymerization of the synthesized zinc organic complex with the methyl methacrylate (MMA) monomer.2-(2-hydroxy phenyl) benzothiazole was as luminescence ligand in the zinc organic complex. Finally, the white light was obtained by blending the dysprosium polymer phosphor and zinc polymer phosphor. (1) The reactive Dy(Ⅲ)-containing complex Dy(4-BBA)2(TPPO)2(UA) was synthesized employing4-Benzoylbenzoic acid (BBA), triphenylphosphine oxide (TPPO) and10-undecenoic acid (UA) as ligands. The copolymer MMA-co-Dy(4-BBA)2(TPPO)2(UA)(PMDy) was synthesized by free radical copolymerization of the reactive complex with the methyl methacrylate (MMA) monomer. The fluorescence results show that with the excitation wavelength of365nm, dysprosium organic complex displayed the characteristic peaks of the Dy(Ⅲ) ions at480nm and572nm, and the color coordinates were calculated as (0.338,0.403) according to the emission spectrum, being locating in the white yellowish light area. When the complex content exceeded0.41%(wt%), the luminescence intensity of the dysprosium polymer maintains the luminous intensity of the complex. Its color coordinates were x=0.315, y=0.369, closing to the white light (0.33,0.33). TG and DSC analysis show that initial decomposition temperature of the polymer was at228℃, the glass transition temperature increased from105℃to132℃, compared to PMMA.(2) Zinc organic complex Zn(BTZ)(UA) was synthesized employing2-(2-hydro-xyphenyl) benzothiazole(BTZ) as the first ligand, undecylenic acid as active ligand and the zinc(Ⅱ) ion as the center ions. Copolymer PMZn was obtained by free radical copolymerization of Zn-containing complex with methyl methacrylate. The fluorescence results show that the complex Zn(BTZ)(UA) presented broad emission at the473nm and its color coordinates were x=0.143, y=0.251, being located in the blue area. Compared with the complex, the emission peak of the polymer shifted to450nm. Thermo-gravimetric analysis reveal that, the initial decomposition temperature of the polymer PMZn was223℃, and increased103℃compared with the complex. The polymer PMZn can be used as blue light component in white light.(3) Adjusting the mixing ratio of PMDy and PMZn, five different blend proportions of phosphors were obtained. The fluorescence results show that the blend occurred the broad emission at450nm attributed to copolymer PMZn; emitted narrow peaks at480nm and572nm for Dy(Ⅲ) characteristic peaks in the polymer PMDy. When the molar ratio of PMDy:PMZn was22:1, the blend emitted nearly white. TGA show that the initial decomposition temperature of the blend phosphor was219℃, meeting the temperature requirements of the LED as light-emitting layer. Blending phosphor PMDy/PMZn is a potential white phosphor.