Nonradiative Transitions A Qualitative Approach

Nonradiative Transitions A Qualitative Approach A. The Weak-Coupling Case 

Nonradiative transitions in the weak-coupling approximation are probably the best understood nonradiative processes. The experimental data relate mainly to the rare-earth ions, as far as their sharp-line transitions are considered (i.e., intra-4/ configuration transitions). The topic has been discussed in many books and review papers (see also above) (11,12). 

Ions like Eu and Tb may emit from higher excited states Eu + not only from Dq (red), but also from Di (green) and D2 (blue). However, this depends critically on the host lattice. In Y203-Eu , for example, all these emission are observed, since comax 600 cm . In borates and silicates, however, they are not. 

This can be well studied by laser spectroscopy. An example is NaGd-Ti04 Eu (93). The time dependence of the Eu + emission in NaGd-Ti04 on excitation into the level of Eu is as follows 10 /ns after the 

The Tb ion may not only emit from D4 (green), but also from (blue). AE is about 5000 cm , much larger than in the case of Eu. Diluted Tb systems, therefore, always show some blue Tb emission, unless comax is very high. 

---