Energy Transfer to the Trivalent REE

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 R.E. ion. 

Exciting closed shell transition metal complexes such as tungstates, molybdates, vanadates, titanites etc. This way of excitation and its transfer to the rare-earth elements has been known since the late fifties. 

Energy transfer from strongly absorbing R.E. due to f-d, or charge transfer band. 

The energy levels scheme of trivalent REE may be seen in Eig. 5.1 and excitation 

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