Electric dipolar transitions

The calculated lifetimes (Table 4) are several powers of ten larger then those corresponding to usual electric dipolar transitions (10- -10 s). They constitute therefore true predictions which require special techniques of measurements that were available only in recent years. 

Table 7. Spontaneous radiative lifetimes Xy j (s) of the A and A 11 bands via A->A in and A IH- X l + electric dipolar transitions...

The spectroscopy of the SD0 level is also a valuable tool to investigate the point symmetry of Eu3+ ions in materials. It is well-known that the 5D0 - 7F2 transition is electric-dipole in nature, while 5D0- -7Fi shows a magnetic-dipole character. 5D0-> 7F2 is totally forbidden in presence of an inversion center and it is allowed in the opposite case. Usually, in vitreous phases, where the symmetry is low, electric dipolar transitions exhibit the strongest intensity. The fluorescence spectra displayed in Fig. 8 show that both transitions have about the same intensity indicating that Eu3+ ions are in high-symmetry sites in fluorozirconate glasses, relatively to oxide glasses. 

Comparing the vibrational A lifetimes issued from both decay mechanisms (Tables 7 - 8), it is readily seen that the electric dipolar transition decay is always slightly favoured. A similar conclusion holds for the A n state but, as expected, the vibrational transition probabilities are much larger for the dipolar decay which lead to much smaller vibrational lifetimes with respect to those via the cascade mode of decay, the differences amounting to five to six powers of ten (Table 7 - 8). 

In the visible and ultra-violet region of frequencies v (the wave-number a is t>/c) the electric dipolar polarizability a is connected with a summation over all the k excited states to which the transition has the oscillator strength P ... 

However, it is worthwhile to realize that a direct relation between the oscillator strength P of a given transition and its half-life tj/2 as electric dipolar emission was found by Einstein in 1917. If the excited level with energy E2 and degeneracy (number of mutually orthogonal states) e2 decays to the lower energy level Ex (not necessarily... 

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