Project A5: Collective formation of a many electron-hole pair state from absorption of a high-excess energy, single photon.

For large energy differences between the absorbed photon and the energy gap
(e.g., UV-light and NIR-emitting nanoparticles), the excited electron-hole pair
has several Coulomb-mediated relaxation pathways. We plan to promote a
theory-experiment study to clarify the different relaxation pathways to promote
either the one-photon to n=1 exciton emission in the UV or the one-photon to
n>1 NIR exciton transformation. In this process, a non-equilibrium situation is
provided by generating a non-thermal electron-hole distribution, interacting via
its nonlinear Coulomb interactions among the carriers. During the relaxation,
dissipative processes are induced by the electron-phonon interaction. In theory,
we will apply a density matrix description within a dynamics controlled truncation
and correlation expansion to determine the population dynamics. Experimentally,
different relaxation pathways are distinguishable by measuring the dynamics of
the absorption bleaching as a function of exciting photon energy. The planned
pump-probe experiments to study the impact of Coulomb interaction and quantum
confinement on the charge-carrier dynamics will be performed as a comparative
study of (i) a 2D- and 0D-system of same material (e.g., GaAs), (ii) two different
0D-systems with different gap energy and/or same/different LO-phonon energy,
and (iii) a 0D-system of NIR-emitting nanoparticles under external electrical field.

Project leaders: Prof.Dr.  U. Woggon [1],   Prof.Dr.  A. Knorr [2]