Excitonen

Exzitonen, known in English as excitons, are quasi-particles that arise when an electron in a material is bound to the positively charged hole left behind after excitation. In semiconductors and insulators, the Coulomb attraction between the excited electron and hole can create a bound state with an energy below the band-gap edge, allowing energy transport without net charge.

There are two broad classes. Frenkel excitons are tightly bound and localized on a single lattice site, common in molecular crystals and organic semiconductors. Wannier–Mott excitons are more delocalized, with radii larger than a lattice constant, typical of inorganic semiconductors; they have smaller binding energies and can be described by hydrogen-like models.

Exzitonen can migrate by diffusion or coherent transport, enabling energy transfer over distances longer than individual particle motion would permit. They have finite lifetimes, from picoseconds to nanoseconds, depending on recombination pathways. They can decay radiatively, emitting photons, or non-radiatively through phonons or defects. At high densities, exciton–exciton interactions can lead to annihilation or dissociation.

Experimental techniques include absorption and photoluminescence spectroscopy, time-resolved measurements, and near-field or angle-resolved photoemission. In devices, exciton dynamics influence the efficiency of light-emitting diodes, solar cells, and photodetectors. In microcavities, coupling exzitonen to photons can form exciton-polaritons, enabling novel light-matter phenomena.

Terminology note: the conventional English term is exciton (plural excitons). The form excitonen is used in some languages as a variant plural or in specific contexts; readers should map it to the same underlying concept.