Lanthanide vibronic

The calculations do not attempt to model detailed vibronic structure. The simulated spectra are produced by superimposing a Gaussian band on the zero-phonon line, rather than calculating the individual vibronics. For the emission spectra of lanthanides in LiYF4, individual vibronic features are not clearly resolved (see fig. 7), and the calculated broad vibronic bands give a reasonably good description. By contrast, for lanthanides in YPO4, the offset between... 

Gruen [80] found that the vapor of Ndl3 of D3h symmetry with a spherical harmonic k = 1 does not transform as a totally symmetric representation. This is a case that cannot be explained on the basis of symmetric representation of hypersensitivity. Since Ndl3 vapor molecules are in a relatively homogeneous dielectric, the pseudoquadrupole mechanism is not operative. A vibronic mechanism including covalency has been advanced to explain the origin of hypersensitivity in lanthanide complexes. 

When the lanthanide ion is surrounded by voluminous polarizable anions like chloride, bromide, or sulfide ions, the Stokes shift is generally small. At low temperatme, a zero-phonon line is present in absorption and emission spectra, in addition to the band corresponding to transitions involving absorption or emission of phonons (vibronic transitions). Low... 

As described previously, nonradiative decay due to solvent interactions can severely reduce lanthanide luminescence through energy dissipation by vibronic modes, with the O—H oscillator being the most common and eflBcient quencher. However, if these O—H oscillators are replaced with lower-frequency O—D oscillators, the eflBciency of vibronic deactivation decreases substantially. Therefore, the rate constants for luminescence lifetimes (th o) of lanthanide excited states in water or alcoholic solvents are often much shorter than those in analogous deuterated solvents (td o)- This property can be utilized to determine the degree of solvation for luminescent lanthanides. 

Vibronic Mechanism. j0rgensen and Judd (53) considered and rejected the vibronic mechanism as the source of the observed hypersensitivity for lanthanide ion solutions since the calculated magnitude of t2 was too small by a factor of 10 compared with experimental values of t2. 

Abstract A brief review of my work with Carl Ballhausen in 1967-1968 and subsequent work. The assignments of the vibronic sidebands in the emission spectra of chromium ammine complexes are given with some comments on the Jahn-Teller effect in the emissive state. Energy transfer and cross relaxation phenomena are discussed and the shell model for this processes in lanthanide elpasolites is presented... 

We therefore developed a much simplified, but mathematically exact, version of a shell model which is particularly suitable for the analysis of cross relaxation in high symmetry systems such as the lanthanide elpasolites. Since the vibronic structure in the emission and absorption spectra of these compounds is both intense and broad (relative to the electronic origins), there are many cases where the vibronic structure of one electronic transition in emission overlaps with the vibronic structure of another electronic transition of a chemically identical ion in absorption. The emission of the excited ion may then be partially quenched by energy transfer. Implicit in this formulation is the assumption that the interionic coupling is weak compared with the vibronic coupling this is certainly true for the lanthanide elpasolites where the lanthanide ions are separated by distances of more than 0.7 nm. We refer to this process as cross relaxation by the electric dipole vibronic-electric dipole vibronic (EDVEDV) mechanism. 

This review has summarised and commented upon the literature up to the end of 2002. The electronic spectra of elpasolite systems are complex and mainly vibronic in character. Whereas the major features can be interpreted in terms of localized moiety-mode vibrations, our understanding of the fine structure requires a more detailed investigation of the lattice dynamics of these systems in the future. One- and two-photon studies of certain lanthanide elpasolite systems have recently enabled extensive energy level datasets to be obtained, and the parametrization of these has revealed the need for the incorporation of other interacting configurations into the calculation. 

Alkaline-earth fluorides have been the principal hosts for divalent lanthanide lasers. These are relatively soft, optically isotropic materials. Lanthanides enter the alkaline earth sites substitutionally without charge compensation. Because these sites have inversion symmetry, only magnetic-dipole or vibronic transitions are allowed between 4f states. These are weak and the resulting radiative lifetimes are long. In comparison, the radiative lifetimes of 5d->4f transitions, which are parity allowed, are-short. The 4f->5d transitions are broad and thus provide good absorption bands for optical pumping. 

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