Non-radiative losses

Stokes shift. Another possibility is that the optical excitation occurs from a negatively charged (D ) gap state to a D gap state, where there is initial non-radiative loss of energy to a stable D configuration. Photoluminescent emission takes place bringing the electron back to the D centre. This is illustrated in Figure 8.16 schematically. This type of... 

Figure Pl.l Conceptual laser resonator, including optional components for wavelength selection and temporal shaping of the laser output. Intrinsic photon loss processes, which reduce the useful laser radiation absorption, spontaneous emission and non-radiative losses in optical media scattering losses at resonator components imperfect reflection/ antireflection coatings...

Fluorescence quenching is due to non-radiative loss of energy from the excited state as a consequence of either collision with a quencher ion (or molecule) in solution or by formation of a non-fluorescent or poorly fluorescent fluorophore-quencher complex. In both cases the quenching process follows the Stem-Volmer equation ... 

Besides the mentioned thermodynamic losses, there always exist kinetic losses arising from the competitive non-radiative quenching of the excited state. For instance in photovoltaic devices, the undesired thermal recom-... 

Figure 2.11 Morse curve for an excited molecule. The energy required for excitation (A) is lost as the molecule returns to the ground state but only the energy lost between states (C) may be emitted as radiation. Energy losses due to internal rearrangements (B and D) are non-radiative.

Primary energy loss pathways include radiative and non-radiative deactivation of the dye sensitizer (Process 6), recombination of the conduction band electrons by the oxidized sensitzer (Process 7), or recombination of the conduction band electrons by the the oxidized form of the redox system (Process 8). 

Table 1 Radiative and non-radiative voltage losses in polymer fullerene solar cells...

Diethylamino-4-methylcoumarin is used to sensitize a weakly fluorescent second material in a mixture designed for use as an in situ flaw detector in metal surfaces. The energy absorbed by the coumarin is transferred to a second component with little energy loss by non-radiative processes. The blue fluorescence of the coumarin is replaced by the yellow-green of the other component, to which the eye is more sensitive. 

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)... 

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