Intraconfigurational transition intensities

Europium intraconfigurational transition intensities and emission quantum yields... 

How is the parity selection rule relaxed Vibrations have only a very weak influence. For interesting consequences of this influence the reader is referred to Ref. [13]. Of more importance are the uneven components of the crystal-field which are present when the rare earth ion occupies a crystallographic site without inversion symmetry. These uneven components mix a small amount of opposite-parity wave functions (like 5d) into the 4/wavefunctions. In this way the intraconfigurational 4/° transitions obtain at least some intensity. Spectroscopists say it in the following way the (forbidden) 4/-4/transition steals some intensity from the (allowed) 4/-5rftransition. The literature contains many treatments of these rare earth spectra, some in a simple way, others in considerable detail [1,16,17,18,19]. 

The spectral intensities of f-f transitions in lanthanide compounds are discussed at length in chapter 167. Professor Christine Gorller-Walrand and Dr. Koen Biimemans, from the Catholic University at Leuven, have presented an exhaustive consideration of the unique appearance of intraconfigurational electronic transitions in f-type materials, particularly the lanthanides. This didactic presentation follows one, by the same authors, on the crystal-field splitting that provides information on the symmetry of the R site presented as chapter 155 of Volume 23. 

Generally, the room temperature emission spectra of Ln species show incompletely resolved stmcture within the peaks. However, an advantageous attribute of luminescent Ln complexes is the dependence of this emission spectral form on the specific coordination environment of the ion. This sensitivity arises from the selection rules associated with intraconfigurational (4f-4f) electronic transitions the selection rules for forced electric dipole transitions are relaxed due to 5d and 4/orbital mixing. In reality the majority of the complexes included for discussion here are non-centrosymmetric, low symmetry species and the relative intensities of the 4/-4/transitions are generally determined by the induced electric dipole transition selection rules. It should also be noted that visibly emissive Eu also possesses a magnetic dipole transition, F, whose intensity is relatively independent of the coordination environment [1,9]. 

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