Exciton deep-trapped

It is possible that partially decrease of selected energy of EAi+ = 0,3 keV. Possibly, the a E) drop is connected with the formation of Cd-C complexes, which create the deep traps for capture of free electrons. The appearance of such traps in energy range of HOMO-LUMO confirms in the formation of the new bands of the emission of excitons for the Cd-C6o mixture... 

Webber and Swenberg (82) worked out a master equation theory for excitonic annihilation processes in low dimensional, finite lattices. This theory seems to describe well the process for polymers with few or shallow traps, as P2VN, but not for those containing many relatively deep traps, as PVCA. Finally, a list of those features which at the present time prevent a full understanding of T-T annihilation in dilute, solid solutions of aromatic polymers... 

Fig. 7, Representation of lattice statistics for polymer exciton annihilation. The following symbols are used Q = deep trap H = reflecting barrier - = available exciton migration length v, = fast and slow hopping num-...

We mentioned the main models for generation, transfer, and recombination of the charge carriers in polymers. Very often, these models are interwoven. For example, the photogeneration can be considered in the frame of the exciton model and transport in the frame of the hopping one. The concrete nature of the impurity centers, deep and shallow traps, intermediate neutral and charged states are specific for different types of polymers. We will try to take into account these perculiarities for different classes of the macro-molecules materials in the next sections. 

Below 4 K the traps are effective. Around 4 K, however, the shallower traps (like Zn (3 nn). Mg (3 nn)) begin to lose their trapped excitation energy by thermally activated back-transfer to the exciton level. From here the energy may be trapped by deeper traps. Finally all the emitting traps are emptied and only the deep, non-emitting traps are operative. As a consequence the luminescence has been quenched. These quenching traps may be Ni and/or Fe ions (see Fig. 11). 

In molecular solids the molecules cannot move around freely, but they are trapped in relatively deep potential wells, caused by the intermolecular potential. In these wells they can vibrate and since the vibrations of individual molecules are coupled, again by the intermolecular potential, one obtains collective vibrations of all the molecules in the solid, called lattice vibrations or phonons. Phonons associated with the center of mass motions of the molecules are called translational phonons, phonons associated with their hindered rotations or librations are called librons. The degree of hindrance of the rotations may vary. If the molecules have well-defined equilibrium orientations and perform small amplitude librations about these, one speaks about ordered phases. If the molecular rotations are nearly free or if the molecules can oscillate in several orientational pockets and easily jump between these pockets, then the solid is called orientationally disordered or plastic. Several molecular solids may occur in each of these phases, depending on the temperature and pressure they undergo order/disorder phase transitions. Also the intramolecular vibrations are coupled by the intermolecular potential, via its dependence on the internal coordinates. The excitations of the solid associated with such vibrations are called vibrational excitons or vibrons. 

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