Objective
Mollar aggregates play an essential role in Nature (photosynthesis: light-harvesting complex), are of great importance in industrial applications (photographic film: J-aggregates in colour film), and their nonlinear properties are currently of great interest in optical communications systems, so understanding their intrinsic behaviour will have both scientific and technological implications.
The purpose of the project consists in the elaboration of a complete energetic and dynamic scheme of electronic energetic relaxation channels in three-dimensional (3D), two-dimensional (2D), and quasi one-dimensional (1D) crystals and in the statement of essential distinctions in the character of electronic relaxation processes, related to dimensionality. Main attention is focused at a most complicated and interesting aspect of energetic relaxation in solids - exciton self-trapping which generally requires the creation of an initial lattice deformation, large enough to be supported by the trapped exciton. In other words, exciton self-trapping is attended by overcoming an energy barrier. Such barriers can be overcome via a variety of relaxation processes, essentially dependent on dimensionality. Traditional notion on these processes cannot describe the current experimental data. For the 3D case, the conventional approach predicts too large energy barriers and an actual blocking of exciton self-trapping, in contradiction to experiment. For the 1D case, it is conventionally considered that no barrier exists, since an exciton can be trapped by an arbitrarily small 1D potential well. But in real quasi 1D systems the existence of self-trapping barrier is evidenced by the well-pronounced free-exciton luminescence.
The authors of the project have a significant advance in the elucidation of this complicated contradictory picture. It was shown, first, that in fact a deformation threshold and, hence, the barrier of self-trapping exist for all dimensionalities. Second, in the 3D and, probably, in 2D cases the barrier can be lowered and even eliminated due to the branching of relaxation paths in the coordinate or quasi-momentum space. Within the project, these mechanisms will be thoroughly explored experimentally and theoretically.
Another aspect of the planned researches is connected with an expansion of the class of examined stances. The authors plan to change from model rare-gas crystals, which were used as model systems for studying relaxation processes in solids, to a broader class of materials with another type of structure and another (pico- or femto-second) time scale of electronic processes. In particular, a knowledge, obtained with the use of model systems at low temperatures, will be extended as applied to new organic materials (e.g. J-aggregates and conjugated polymers) with a strong nonlinear and fast response, which have promising applications in modern optical communication nets and information processing systems.
The research groups of M. Ainbund, Y. Bigot, K. Kemnitz, Yu. Malyukin, A. Ratner, and G. Zimmerer have a considerable advance and unique possibilities for solving the totality of stated problems involving a broad class of materials with 1D, 2D, and 3D electronic structure and electronic relaxation processes of different time scales. The 3D case has been experimentally explored by the research group of G. Zimmerer on model rare-gas crystals. The 1D and 2D systems with the pico- and femto- time scales are intensively studied by the research groups of K. Kemnitz, J. Bigot, Yu. Malyukin and M. Ainbund. A. Ratner has significant theoretical results in the field of polaronic processes in solids. As a result, a complete energetic and dynamic scheme of polaronic states in 3D, 2D and 1D systems will be reconstructed. The system of energy levels of self-trapped excitonic states and energy barriers will be ascertained. The mechanisms of overcoming the barriers, including the branching of energetic relaxation paths for 3D and 2D cases, the role of structure pliarities and thermal activation, will be elucidated. Essential distinctions in the character and rate of electronic energetic relaxation between a quasi-one-dimensional system and three- or two-dimensional crystals will be stated, theoretically described, and used for the explanation of a variety of unusual experimental regularities. The obtained knowledge will form a physical basis for the prediction and control of operation properties of organic films, prospective for modern technologies (films with high nonlinear response, used in optical communication systems and films, used as high-sensitive photographic materials).
The results of the project will promote the development of modern optic communication nets and film technologies in the Ukraine.
Topic(s)
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12247 Berlin
Germany