Metal luminescence efficiency

Eu and Tb complexes of cage-type ligands 77 5.3. Metal luminescence efficiency 106... 

In electroluminescence devices (LEDs) ionized traps form space charges, which govern the charge carrier injection from metal electrodes into the active material [21]. The same states that trap charge carriers may also act as a recombination center for the non-radiative decay of excitons. Therefore, the luminescence efficiency as well as charge earner transport in LEDs are influenced by traps. Both factors determine the quantum efficiency of LEDs. 

Studies in these fields [16] have shown that transition metal complexes may play the role of sensitizers both in the photoinduced processes schematized by Eq. 15 and in the light generating processes schematized by Eq. (16). In the first case, the complex can be called a light absorption sensitizer (LAS), while in the second case it can be called a light emission sensitizer (LES). High luminescence efficiency is a useful property for a LAS, and a necessary requirement for a LES. 

If d>M cannot be measured, it may be substituted, as in Eq. 2, by the efficiency of the metal luminescence (i/M), which is derivable from Eq. 3. Since in this study the radiative (kr), and nonradiative (kar) rate constants are calculated from the experimentally obtained lifetimes, Eq. 3 may be replaced by Eq. 4 on the assumption that the decay of the metal emitting state in D20 at 77 K is purely radiative. 

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