Preparation And Performance Research On Trichromatic Block Copolymers Phosphor In WLED

As a potential candidate for replacing conventional incandescent and fluorescent lamps, white-light emitting diodes (WLED) have attracted considerable interest in recent years owing to the advantages of high efficiency, low energy consumption, and their environmental-friendly characteristics. The research on the phosphors is particularly important to realize white light LED, and at present, the main technology measure is phosphor-converted white LED. It is going to be main method in the future to achieve white LED by stimulating tricolor phosphor.The green light composition plays an important role in realization of white LED, so we preparate a green phosphor with outstanding fluorescence properties and thermal stability. In this paper, we report the synthesis of block copolymers of styrene and RGB (short for Red/Green/Blue) rare earth complex monomer by RAFT, paying particular attention to the luminescent property. The main research results are as follows:(1) A reactive Tb(Ⅲ) complex with p-aminobenzoic acid (p-ABA) and methacrylic acid (MAA) as ligands was synthesized. IR and UV-vis analysis indicates that two ligands have been coordinated with terbium ions. The fluorescence analysis shows that the emission peaks of the complex located at489,544,586,608nm, and were corresponded to the emission of Tb(Ⅲ) ion. Based on the data from fluorescence emission, the CIE coordinates were calculated as (0.239,0.431). Thermogravimetric analysis indicates that the complexes keep stable up to341℃and the velocity reached its maximum at about379℃, which exhibits excellent thermostability. (2) Green light copolymers, PMMA-Tb and PS-Tb, were synthesized by copolymerization of Tb(Ⅲ) complex with the methyl methacrylate and styrene, separately. The mole ratio of rare earth complexes and polymer is1:200, so the infrared spectra of both copolymer mainly reflect characteristic peaks in polymer. UV-vis analysis indicates that the maximum UV absorption wavelength of PMMA-Tb shifted toward long wavelength compared with Tb(Ⅲ) complex. The UV absorption showed a strong peak at258nm, because of the benzene ring structure of PS-Tb. And the physical presence of a strong UV absorption in the Tb complex, so that PS-Tb significant UV absorption enhanced comparing to PS after300nm. Tb (Ⅲ) ion characteristic emission is found in the fluorescence spectra of PMMA-Tb and PS-Tb. Using the data form both copolymer’s fluorescence emission, the CIE coordinate was calculated as (0.272,0.601) and (0.275,0.514), which both are closest to green-light region. But Stokes shift of PS-Tb decreased12nm than PMMA-Tb’s, which indicates that the former is smaller than the energy loss in the non-radiative transition process. Thermogravimetric analysis shows that heat decomposition temperature of PS-Tb was increased about110℃than that of PMMA-Tb, as a result, PS-Tb has a more stable thermal performance. As a word, We chose the PS as the polymer matrix to preparate trichromatic block copolymers phosphor.(3) Trichromatic block copolymers phosphor in white-light was synthesized.As bonded to the polymer matrix of small amounts of rare earth complexes, infrared analysis and UV analyzes were mainly characterized by absorption characteristics of the styrene polymer. GPC analysis showed that all the curves in diagram are unimodal and narrow. The linear relationships between respective ln([Mo]/[M]) and polymerization time demonstrated the chain growth was a’living’ process and block copolymers was successfully synthesized. Each feature emission observed from red fluorescence spectroscopy of rare earth complexes Eu(TTA)2(phen)MAA, green that of rare earth complexes Tb(p-ABA)3(MAA)2, and blue that of complexes Be(BTZ)(MAA), and the fluorescence intensity are all enhanced. The CIE coordinates were calculated as (0.333,0.315), and located at white-light region. The trichromatic block copolymers phosphor was not decomposed untill363℃, and the velocity reached its maximum at about408℃. And the glass transition temperature Tg was281℃, 150℃higher than that of the blended white-light copolymer phosphor. Excellent fluorescence properties and thermal stability makes it an ideal tricolor block copolymer phosphor in white LED.