为了研究配体能级与稀土离子最低激发态能级的匹配程度对所形成的稀土配合物荧光性能的影响, 以邻氟苯甲酸(2-FBA)为第一配体, 邻菲咯啉(phen)为第二配体分别制备两种稀土铽配合物Tb(2-FBA)3·2H2O和Tb(2-FBA)3phen。 元素分析和红外光谱表征了两种配合物的分子组成。 相同浓度的紫外吸收光谱表明, Tb(2-FBA)3phen的第二配体phen替代第一配体2-FBA吸收了部分紫外光。 相同浓度的液体荧光光谱表明, Tb(2-FBA)3·2H2O的荧光发射强度高于Tb(2-FBA)3phen的荧光发射强度。 由于Tb(2-FBA)3·2H2O分子结晶水中的O—H振动会大大消耗配体所吸收的能量而使荧光强度大幅度下降; 2-FBA配体在273 nm的吸收峰所对应的三重态能级必然与能级5D4的匹配程度会更差。 在这种情况下Tb(2-FBA)3·2H2O的发射强度依然高于Tb(2-FBA)3phen的发射强度, 充分说明了第一配体2-FBA与Tb3的最低激发态能级5D4的匹配程度要好于phen与Tb3+的最低激发态能级5D4的匹配程度。 通过结合紫外吸收光谱和荧光光谱对稀土配合物的配体能级的定性分析, 可以初步了解不同类型配体对荧光性能的贡献程度。

Tb(2-FBA)3·2H2O and Tb(2-FBA)3phen were synthesized using o-fluoro-benzoic acid (2-FBA) as the first ligand, and 1,10-phenanthroline (phen) as the second ligand. Elemental analysis and IR spectra were employed to characterize the molecular composition of the two kinds of lanthanide complexes. The UV absorption spectra with same concentration show that the second ligand phen of Tb(2-FBA)3phen absorbs the portion of the UV light instead of the first ligand 2-FBA. Liquid fluorescence spectra with same concentration show that the fluorescence intensity of Tb(2-FBA)3·2H2O is higher than that of Tb(2-FBA)3phen. The analytical results show that the energy level of 2-FBA matches the lowest excited state energy level of Tb3+ (5D4) better than that of phen. The O—H oscillation of the crystal water in Tb(2-FBA)3·2H2O will greatly consume the absorbed energy by ligands, and cause the fluorescence intensity of Tb(2-FBA)3·2H2O significantly decline. The energy level of triplet state of the first ligand 2-FBA corresponding to the absorption peak 273 nm has poor matching degree with the 5D4 energy level of Tb3+. In this case, the emission intensity of Tb(2-FBA)3·2H2O is still stronger than that of Tb(2-FBA)3phen. It illustrates that the energy level of the triplet state of the first ligand 2-FBA corresponding to 252 nm has much better matching degree with the lowest excited state of 5D4 energy level of Tb3+ than that of phen. It is the only way to compensate for energy loss by thermal vibration of water molecules and low energy transfer efficiency for poor matching degree between the energy level of corresponding to 273 nm of the first ligand 2-FBA and 5D4 energy level of Tb3+. By combining UV absorption spectra with fluorescence spectra of lanthanide complexes to qualitatively analyze energy level of ligands, the contribution of different types of ligands to the fluorescence properties can be preliminarily understood.