Abstract
Energy shifts of 4f 6 states of Eu 3+ in matrices, and phonon sidebands, linewidths and luminescence decay of Eu 3+ in Ln 2O 2S (Ln=Lu, Y, Gd and La) have been studied. The charge transfer state (CTS) of Eu 3+ is described by a model in which a hole is transferred from Eu 3+ to ligands. Septet states obtained from the 4f 7( 8S) + hole configuration of CTS interact with the 7F term of the 4f 6 configuration. This effect causes downward shifts of 7F J states in matrices. Diffuse charge distributions for 7F J states due to the mixing with CTS make the curvatuve of their adiabatic potential curves be smaller than that for 5D J' . Such a difference in the potential curves between 7F J and 5D J' causes broadening of the absorption lines compared with the corresponding emission linewidths in Y 2O 2S. A dynamic Jahn-Teller model is proposed for the concentration-enhanced phonon sidebands accompanying 4f-4f transitions. The vibronics appear only in the excitation spectra and not in the emission spectra. Spectral distributions of the effective density of phonon states are obtained from the observed phonon sidebands for Ln 2O 2S: 5%Eu. The phonon spectra indicate delocalization of the 4f orbitals of Eu 3+ with increasing the host-cation radius. The observed lifetimes of 5D 0 show a decrease in the same order due to decrease in the 4f-CTS mixing.
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