Transitions intraconfigurational

The intraconfigurational transitions of the rare earth ions (4/n) are examples of ions which, even in solids, show sharp lines in their spectra. The width is of the order of wavenumbers and is at 4.2 K usually determined by inhomogeneous broadening. These lines are true zero-phonon lines. The vibronic transitions belonging to these lines are weak and often overlooked. 

In this paragraph we will discuss two types of optical transitions in the transition metal ions first the intraconfigurational dn transitions, second the interconfigurational charge-transfer transitions in complexes with a d° central metal ion. 

The vibronic transitions in the intraconfigurational dn (crystal-field) transitions have been discussed at length elsewhere (see e.g. Ref. [1]). We concentrate here on new emissions situated in the infrared spectral region and on information from vibronic spectra on distortions in the excited state. 

All three of these problems tend to be resolved when bands due to intraconfigurational transitions are used. In six-coordinate, approximately Oh complexes these are l2g t2g and eg -> eg transitions, quite often accompanied by a spin flip, and therefore forbidden. In contrast to t2g - eg transitions, these are usually numerous, narrow (because the excited state resembles the ground state), and simple each observed narrow line comprises just one component. The relative abundance of these sharp lines (8 for d3 complexes, for example, and as many as 14 for low-spin d4) is deceptive it is because the also numerous t2g —> eg components cluster under broad bands. 

To date, most of the specific applications of eqs. (4) and (5) have involved considerable simplifications of the complex dependence on geometry and conformation implied in eq. (4), and described above. Some of these simplifications are due to the nature of the molecular system under study. For example, as we will discuss in more detail below, intraconfigurational f f transitions are essentially spherical transitions, and, thus, complications due to photoselected orientational distributions are eliminated, and the emitting sample is essentially isotropic (i.e. independent of orientation). Other simplifications arise when one is concerned with g]um( )- For example, Snir and Schellman have shown that when i abs is parallel to jtem. the geometry dependence in IQ.) and AI(A.) is the same and can be factored out of the ratio [10]. 

Europium intraconfigurational transition intensities and emission quantum yields... 

Deutschbein ". Most of the intraconfigurational 4f transitions in the RE ions, however, cannot be accounted for by the magnetic dipole mechanism, not only because the predicted oscillator strengths are in general smaller than 10 , but also due to the restrictive selection rules on the total angular momentum 7, A7 =0, 1 (0 0 excluded), as far as 7 is considered to be a good quantum number. 

Generally, TL spectra of diketonate complexes are characterized by the metal ion-centered transitions, which exhibit similar position and spectral profiles as those photolu-minescent ones ". The TL spectra of trivalent europium diketonates usually display only those intraconfigurational F] (J = 0-4) transitions which are dominated by the... 

More generally, it has been noted [116] that the oscillator strengths for fully allowed ED MD EQ transitions are in the approximate ratio of 1 10 5 10 6, respectively. However, ED transitions are parity forbidden in the case of f-f intraconfigurational transitions, so that the mechanism which enables such transitions for rare earth ions is via crystal-field mixing of fN wave functions with opposite parity wave functions such as fN-1d due to the odd terms HCP = B, C, (i) with f= 1,3,5,7 (which are usually ignored when... 

We briefly summarize the parameterization schemes for f-electron energy levels, intraconfiguration transition probabilities, and the electron-phonon interaction, and review the current experimental situation for each area. We shall also speculate on potentially fertile areas of future investigation. 

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