CHARGE TRANSFER TRANSITIONS IX RARE EARTH ION COMPLEXES WITH CROWN ETHERS

Author Institution:The weak, sharp f to f electronic transitions of rare earth ions show characteristic crystal field splitting when complexed by crown ethers. Some of these complexes also exhibit structureless bands several thousand $cm^{ -1}$ in width having extinction coefficients of the order of 100. For ytterbium $(Yb^{+3})$ complexed with 15-crown-5 and benzo-15-crown-5, the absorption maxima occurs at $45000 cm^{-1}$ and $31,500 cm^{-1}$ respectively. For europium $(Eu^{+3})$ these bands are shifted about $5000 cm^{ -1}$ to lower energy. The magnitude and direction of this shift, and tee fact that these bands are seen only for the readily reducible ions, leads us to assign the observed transitions as charge transfer bands. The charge transfer band of naphthalene-15-crownl-5 occurs at the same energy as does the band for the benzene derivative. This proves that the charge transfer is not from the aromatic moiety to the ion, but rather from the crown ether oxygens adjacent to the aromatic ring. The relationship between the geometry of the complex and the charge transfer transition moment will be discussed. It appears that the relative energies of the charge transfer states and the fluorescing states of the rare earth ions alter the mechanism for radiation less decay. The rates of fluorescence quenching from the $^{5}D_{0}$ and $^{5}D_{0}$ states of $Eu^{+3}$ are differentially affected ay complexing with the several crown ethers studied