Activation energy crossover temperature

Temperature quenching of broad band emission is usually explained by a simple configuration coordinate model consisting of two parabolas that have been shifted with regard to each other (Fig. 6). This is called the Mott-Seitz model. Nonradiative return from the excited to the ground state is possible via the parabola crossover. Its rate can be described with an activation-energy formula Pnr = C where C is a constant of the order of 10 sec i and AE is the... 

Fig. 6. Configuration coordinate diagram of a luminescent centre. Non-radiative return from the excited state to the ground state is possible via the crossover S. This requires an activation energy AE which can be supplied at higher temperatures. Exc excitation, em emission...

Figure 11. Same as in Fig. 10, but the configurational entropy ScT is normalized by the product of the critical entropy si and the activation energy Ap (estimated from Eq. (42) and the computed crossover temperature 7i). According to Eq. (41), the slope of the resulting curves defines the fragility parameter K. (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas,... 

One study specifically designed for PEFC was reported by Thompson et al.8 They used a direct current to measure the proton conductivity at low temperature. In conjunction with the DSC data, they found the dependency of crossover temperature (temperature where the activation energy changes) on water content and hysteresis between freezing and melting. 

The two-mode model has two characteristic crossover temperatures that correspond to the freezing of each vibration. At temperatures above Tc0 = h(o0/2kB, the rate constant k(T) exhibits its ordinary Arrhenius form, in which the activation energy is determined by the effective barrier height... 

As another illustration, note that above the crossover point Tc the temperature dependence k(T) exhibits an activation energy equal to... 

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