Y^(3+)对水溶液聚合结构中Eu^(3+)的荧光增强作用

Fluorescence Enhancement Effect of Yttrium(Ⅲ) on Europium(Ⅲ) within the Polymeric Structure in Aqueus Solution

合成了两种双功能的配体 2 ,2′,6 ,6′ 四羧基 4 ,4′ 联吡啶 (BDPA)和双 ( 2 ,6 二羧基 4 吡啶基 )硫醚(SDPA)。观察到Y3 + 能明显提高水溶液聚合结构中Eu3 + 的荧光强度。荧光增强机制表明 ,Eu3 + 、Y3 + 和配体所构成的水溶液聚合结构 ,有利于使Y3 + 配合物中的配体所吸收的能量有效地转移给Eu3 + 。

The aim of our work is to produce enhanced Eu 3+ luminescence in aqueous solution by using energy transfer between ligands, which are linked together by Y 3+ without other additives and micelle formation. We synthesized two bifunctional complexing agents 2,2′,6,6′-tetracarboxy-4,4′-bipyridine (BDPA) and bis(2,6-dicarboxy-4-pyridyl) sulfide (SDPA). In this polymeric network the enhancement of Eu 3+ luminescence is based on two factors. First, a great excess of energy donors (ligands) relative to energy acceptors (Eu 3+) was used. Excess of ligands was added to obtain maximum absorption and excess of Y 3+ was added to link the ligands and enhance intersystem crossing to triplet state in these ligands. Secondly, the energy absorbed by ligands coordinated to Y 3+ is transferred toward Eu 3+ via triplet-triplet migration. One Eu 3+ is able to be excited either with the energy absorbed by three ligands coordinated to Y 3+, or by several other ligands coordinated directly. This means that when energy is lost non-radiatively during the energy transfer process from the ligand to the Eu 3+, thus Eu 3+ can still be excited by energy transfer process from other ligands coordinated to Y 3+. The luminescence intensity of the Eu 3+ was plotted against time after mixing of BDPA, Y 3+ and Eu 3+. The growth of the luminescence signal was quite rapid at the beginning, but slowed down 3min later. The SDPA system showed the same phenomenon. The ligand concentration, Y 3+ concentration and pH were optimized. In two systems with different ligands the effect of pH was investigated in the range 3～11. The luminescence signal was observed to be highest at pH 9. The effects of Y 3+ concentration and BDPA concentration on Eu 3+ luminescence were studied respectively. In the case of BDPA, the luminescence intensity of Eu 3+ was highest when the Y 3+∶BDPA ratio was close to the theoretical value 2∶3. When the luminescence intensity of Eu 3+ was plotted against the concentration of Eu 3+, it can be seen that there is a quite good linearity within 1×10 -10～5×10 -7mol/L range, which enables to be a method used for determination of trace amounts of Eu 3+.It can be seen that adding of Y 3+ will increase Eu 3+ luminescence greatly. The enhanced Eu 3+ luminescence is most likely due to the presence of efficient energy migration from the ligands coordinated to Y 3+ to the Eu 3+. The Eu 3+(Y 3+)-BDPA system reached the highest luminescence intensity. It might be the result of several factors. The BDPA has a symmetric, conjugated structure. This structure has the shortest distance between different Y 3+ centers and its triplet energy level is suitable for transferring energy to the resonance level of Eu 3+. It is totally conjugated and planar, which enables the effective energy transfer between ligands. However, the SDPA does not has a conjugated structure, and this may be responsible for the diminished energy transfer compared with that of the BDPA system. The effect of replacing Y 3+ with other lanthanides such as Gd 3+, La 3+ and Lu 3+ was also studied. The sequence of the enhancement is: Gd 3+>Y 3+>Lu 3+>La 3+. It is noticed that Tb 3+ also enhances Eu 3+ luminescence in this polymer structure.