Transference activation energy

A schematic energy-level diagram of Cr3+ and Tm3+ in YAG together with the luminescence and absorption spectra of Cr3+ are shown in fig. 18. Three primary Cr3+ - Tm3+ energy transfer pathways can be identified thermally activated energy transfer from the 4T2 state (4T2 ET), thermally activated energy transfer from the 2E anti-Stokes phonon sidebands (2E anti-Stokes ET), and temperature-independent energy transfer from the zero phonon and Stokes phonon sidebands of the 2E state (2E Stokes ET). 

Direct pumping of poison centers as well as energy transfer from co-activators, and energy transfer from activators all represent an energy loss in the system. In addition, activators and co-activators also have non-radiative decay routes. Because non-radiative decay is usually phonon-assisted, non-radiative decay is exacerbated by increasing temperature and manifests itself by a characteristic temperature at which luminescence is quenched. The crystallographic relations that provide optimum sensitizer -activator energy transfer are outlined by Blasse (9)... 

Moreover, fluorescence characterization of these systems indicated, as previously hypothesized, that ruthenium(II) cationic complexes are able to activate energy transfer processes towards the anionic porphyrins [50]. 

Rempel, U., B. Vonmaltzan, and C. von Borczyskowski (1995). Competition between charge-transfer via superexchange and thermally activated energy-transfer in porphyrinheterodimer-quinone systems. Chem. Phys. Lett. 245. 253-261. 

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