EXCITATION PROCESS OF LUMINESCENCE OF Ce3+ POLYMER COMPLEXES
Li Welian (Changchun institute of Physict, Academic Sinica)T.Mishima G.Adachi J.Shiokawa(Department of Applied Chemistry, Faculty of Engineeirng, Osaka University, Yamadaoka 2-1 Suita, Osaka, Japan)
Energy transfer in rare earth (RE)-organic complexes materials and their luminescence properties have obtained extensive attention in the recent years. Studies of luminescence regarding to polymer compelxes of RE are particularly interesting. We have demonstrated that the energy transfer from the bpy (2,2'-bipyri-dine) to the central Ce3+ ion for the Ce3+-bpy complex solution and reported that the complexation of Ce3+ with the polemers and the fluores cence properties of the compexes in the preceding papers.In this paper, we described relation between the excitation process of Ce3+ fluorescence and the structures for the two complexes. The polymer complexes of Ce3+ are Ce3+-polymethylmethacrylate, Ce3+-PMMA and Ce3+ -poly-(2-methacryloyloxymethy-1, 4, 7, 10, 13,16-hexaoxacyclotodecane), Ce3+-PMAl8.C.6,respectively. 1. Ce3+-PMMA Film ComplexExcitation spectrum of Ce3+ fluorescence (See Fig.1) was corresponding with the absorption spectrum of Ref[ 5] for the Ce3+-PMMA film complex. That is, fluorescence of Ce3+of Ce3+-PMMA complex was obviously observed when the polymer ligand Was excited. Thus, we may concluded that the Ce3+ fluorescence would be due to the energy transfer from the polymer ligand.Fluorescence lifetime of the PMMA ligand was about 1.1ns in the absence of Ce3 + . however, that of the PMMA was descrcascd while Ce3+ ions Were introduced into the polymer film. So an evidence of nonradiative energy transfer from the polymer to the Ce3+ ions was obtained too.On the other hand, decay time at maximum emission intensity of Co3+ ions could be calculated from following formula if the energy transfer of metal organic complex takes placet.Here r1 was fluorescence lifetime of the ligand and t2 was one of the centrical metal ions of the complex. The calculated result (3.6ns) was consistent with the measured one (about 3.6ns). From the absorption spectrum, time-resolved emission spectrum and decay time, the energy-level diagram and possible paths of the energy transfer for the Ce3+-PMMA comples was illustrated, as shown in Fig.4.2. Ce3+-PMAl8.C.6 Powder CmplexThe Ce3+ fluorescence intensities of the Ce3+-PMA18.C.6 complex were monotonously changed with the delay time of the Ce3+ fluorescence, as indicated in Fig.5.The excitation spectrum of the Ce3+ fluorescence was different from that of the PMA.18.C.6 ligand. It is noted that the excitation bands of Ce3+ fluorecence for Ce3+-PMAl8.C.6 complex were situated at 32.0×103 and 38.0×103cm-1, respectively, which were generated from 4f-5d absorption of Ce3+ ions complexed with the PMA18.C.6. Therefore, Ce3+-fluorescence results from the direct excitation of the Ce3+ ions, because the Ce3+ ions were complexed with the polyether group for the Ce3+-PMA18.C.6 complex.From the preceding results we concluded that the difference of the excitation mechanism was accounted for by obviously different nature of the polymer structures. The coordinating groups of the PMMA consits of carbonylic groups, and one of the PMAl8.C.6, however, were composed of the 18.C.6 polyether rings, although the two ligands have the same polymeric main chains.