Energy Transfer Between Two Rare Earth Ions

4 Energy Transfer Between Two Rare Earth Ions 

The above sections summarize the ways in which the electronic f levels of RE ions are populated and depopulated by radiative and non-radiative transitions. As already mentioned the population density of the luminescent levels is generally weak because of the low transition probabilities. However there are other possibilities to increase the luminescence mainly by creating strongly absorbing species that will transfer the energy to the RE ion. The three main ways of such excitation are  

Exciting closed shell transition metal complexes such as tungstates, molybdates, vanadates, titanates, etc. This way of excitation and its transfer to the RE has been known since the late 1950s. The method has been applied to phosphors for luminescent lamps and television screens. There is a vast literature and many reports by Phillips, General Electric, Westinghouse, etc. 

Energy transfer from strongly absorbing RE due to f-d transitions or charge transfer. 

Rare earth ions are especially suitable for energy transfer studies due to their well-defined and narrow electronic levels, to which absorption occurs and from which fluorescence is observed. Symbolically, energy transfer can be written as 

---